Pancreatic acinar cell carcinoma

Pancreatic acinar cell carcinoma is a rare malignant neoplasm of the exocrine pancreas arising from cells with acinar differentiation and enzyme-synthesizing capacity. Although it originates from a cellular compartment that is widely represented in the pancreatic parenchyma, this neoplasm accounts for only a small proportion of pancreatic tumors and differs clearly from ductal adenocarcinoma in its biological profile, molecular features and, in part, response to systemic treatments. Its rarity and the heterogeneity of clinical presentations mean that much of the evidence comes from registries, retrospective series and systematic reviews, making a strongly multidisciplinary diagnostic and therapeutic approach essential.

Clinically, acinar cell carcinoma may present with symptoms overlapping those of other pancreatic neoplasms, such as abdominal pain, weight loss and jaundice in tumors of the head, but it also has features related to enzyme production. Some patients have elevated serum lipase and, more rarely, a hyperlipasemia-related paraneoplastic syndrome with panniculitis, arthralgia and systemic manifestations that may precede diagnosis and complicate the clinical picture. Diagnosis requires high-quality imaging, histologic confirmation and accurate immunohistochemical characterization, which is indispensable for distinguishing the tumor from neuroendocrine neoplasms, poorly differentiated ductal carcinomas and mixed neoplasms.

Treatment centers, whenever possible, on surgical resection with curative intent, complemented by systemic strategies selected according to biological aggressiveness and specific molecular vulnerabilities. Advanced disease may benefit from fluoropyrimidine- and platinum-based multidrug regimens and, in selected cases, targeted therapies guided by actionable alterations. Prognosis is variable and depends critically on stage at diagnosis and resectability. The appreciable risk of recurrence even after radical surgery makes structured follow-up and active management of nutritional and metabolic complications essential.

The epidemiology of pancreatic acinar cell carcinoma is characterized by its low frequency compared with ductal tumors. Its reported proportion varies among series according to inclusion criteria, availability of centralized histologic review and accurate identification of mixed forms. Analyses based on national registries and population-based studies indicate that it is rare but clinically relevant because it may present at a potentially resectable stage and displays biological patterns that differ from ductal carcinoma. It can arise in any pancreatic segment, with an apparently appreciable frequency in the head, although location is not a discriminatory feature.

Demographically, the disease is described most often in adults and older people, with a male predominance in several series, although estimates vary because of small numbers. Pediatric and adolescent cases have also been reported, in whom the differential diagnosis with other rare pancreatic neoplasms and gene-rearranged tumors becomes particularly important. Presentation at an older age is favored by the nonspecific nature of early symptoms and their possible attribution to benign or functional disorders.

The etiologic causes of pancreatic acinar cell carcinoma are undefined, and no exposure has been shown to be necessary and sufficient to cause the neoplasm. The absence of an established etiology requires a clear distinction between causal attribution and observed epidemiologic associations, which in a rare tumor may be affected by selection bias and histologic misclassification.

In this context, risk factors are nonspecific and often mirror those of pancreatic carcinoma in general, without being primary determinants. Cigarette smoking, older age, and metabolic disorders such as diabetes mellitus and obesity are frequently present in pancreatic tumor cohorts but do not define a distinctive clinical profile for acinar cell carcinoma. Chronic pancreatitis may also coexist, but its direct relationship with acinar cell carcinoma is less well defined than for other histologic types and does not support targeted preventive strategies in clinical practice.

From a genetic perspective, a subset of cases harbors alterations in genes involved in DNA repair and genomic instability, with potential implications both for individual predisposition and treatment selection. Germline predisposition, however, is not a constant feature and should be assessed using standard clinical criteria based on personal and family history and tumor-profiling results. Overall, rarity and biological heterogeneity make the epidemiology of acinar cell carcinoma an evolving field in which diagnostic confirmation and accurate histologic classification are integral to the quality of the available data.

For pancreatic acinar cell carcinoma, there are no screening programs for the general population or dedicated surveillance protocols, mainly because of its low incidence and the absence of a noninvasive test with adequate performance. Imaging as a generalized screening strategy is also unsustainable in terms of risk-benefit balance and because of the high probability of unrelated incidental findings, with the potential for an unnecessary diagnostic cascade.

In clinical practice, early diagnosis depends on prompt recognition of symptoms and signs suggestive of organic pancreatic disease. Persistent epigastric pain, unintentional weight loss, recent-onset diabetes or rapid worsening of glycemic control, obstructive jaundice and signs of malabsorption warrant targeted pancreatic imaging. The objective in this setting is not screening for acinar cell carcinoma but timely identification of a potentially treatable pancreatic lesion, followed by histologic definition of its type.

A separate issue is surveillance of individuals at high hereditary risk of pancreatic cancer, who are managed in dedicated programs based on family history and germline mutations. In these settings, surveillance addresses the overall risk of pancreatic neoplasms and precursor lesions and cannot be directed specifically at acinar cell carcinoma, which remains rare even in selected populations. Identification of an acinar tumor in a patient enrolled in surveillance is a possible outcome of the program, not its premise.

Overall, the most rational strategy remains diagnosis guided by clinical suspicion and appropriate assessment of symptoms, using dedicated imaging and histologic confirmation when indicated, while avoiding surveillance approaches unsupported by evidence.

The biology of pancreatic acinar cell carcinoma reflects an exocrine neoplasm distinct from ductal carcinoma, characterized by acinar differentiation and production of digestive enzymes. Malignant transformation occurs in a setting of genomic instability and signaling-pathway alterations that do not reproduce the classic KRAS-dependent profile of ductal adenocarcinoma. This difference is clinically relevant because, in a subset of cases, it creates specific therapeutic vulnerabilities, particularly when DNA-repair alterations or actionable gene fusions are present.

Pathogenetically, alterations have been described in pathways involved in regulating proliferation and differentiation, including the APC/beta-catenin pathway, together with a relatively high burden of structural rearrangements in defined subsets. In particular, some tumors harbor fusions involving genes of the MAPK cascade, such as BRAF or RAF1, with potential therapeutic relevance in selected settings. Another important biological axis consists of alterations in DNA-repair and homologous recombination genes, which may be associated with sensitivity to platinum compounds and, in selected and well-characterized cases, targeted strategies with PARP inhibitors according to principles shared with other HRD tumors.

Molecular features with the greatest clinical impact in pancreatic acinar cell carcinoma

• Absence or low frequency of driver mutations typical of ductal carcinoma, with greater genomic heterogeneity.
• Presence, in subsets, of potentially actionable alterations, including BRAF or RAF1 fusions and other MAPK-pathway alterations.
• Alterations in DNA-repair genes and profiles consistent with HRD in a subset of cases, with implications for platinum-based chemotherapy and selected targeted strategies.
• Possible mixed components with ductal or neuroendocrine differentiation, which modify tumor biology and clinical management.

Histologically, the tumor is composed of cells resembling normal pancreatic acini, with granular eosinophilic cytoplasm due to zymogen granules, acinar, solid or trabecular architecture, and variable degrees of atypia and mitotic activity. Demonstration of acinar differentiation often requires integration of morphology and immunohistochemistry, especially in poorly differentiated tumors or those with inconspicuous cytoplasmic features, in which the differential diagnosis with poorly differentiated carcinomas and neuroendocrine neoplasms is critical.

Immunophenotype useful for confirming acinar differentiation

• Positivity for exocrine enzyme markers such as trypsin, chymotrypsin and lipase, which are often decisive for establishing acinar lineage.
• Variable expression of markers such as BCL10 and cytokeratins, requiring extended panels in poorly differentiated cases.
• Absent or nondominant expression of neuroendocrine markers, useful for distinguishing well-differentiated neuroendocrine tumors and neuroendocrine carcinomas when integrated with morphology and proliferative index.

A distinctive biological feature is the capacity for clinically relevant enzyme secretion in some patients. Hyperlipasemia may be associated with panniculitis caused by subcutaneous fat necrosis and with articular manifestations, producing a paraneoplastic syndrome that, when present, points toward this histologic type and may serve as an indicator of tumor burden and biological activity. Overall, the pathogenesis of acinar cell carcinoma lies at the intersection of exocrine differentiation, heterogeneous genomic alterations and possible therapeutic vulnerabilities, requiring accurate characterization especially in advanced disease.

The clinical manifestations of pancreatic acinar cell carcinoma are often nonspecific and overlap those of other pancreatic neoplasms. Persistent epigastric or back pain, weight loss, anorexia and fatigue are common, with variability according to tumor location and local infiltration. Tumors of the pancreatic head may cause obstructive jaundice with dark urine and pale stools, whereas body-tail lesions may be dominated by pain and systemic symptoms, sometimes with a later diagnosis because jaundice is absent.

Exocrine pancreatic insufficiency may present with steatorrhea, bloating and malabsorption, particularly with ductal obstruction, surgical resection or extensive parenchymal replacement. Recent-onset diabetes mellitus or rapid destabilization of glycemic control may accompany the disease, reflecting metabolic stress, inflammation and loss of endocrine function. In some patients, the initial presentation may be dominated by thromboembolic events or systemic signs of advanced disease, such as hepatomegaly and right upper-quadrant pain due to liver metastases.

A distinctive, although inconsistent, feature is a possible syndrome related to hyperlipasemia, in which excess circulating lipase is associated with panniculitis characterized by painful subcutaneous nodules, adipose-tissue necrosis, arthralgia or polyarthritis and, occasionally, eosinophilia. This syndrome may precede the diagnosis and requires an assessment integrating clinical findings, enzyme measurement and imaging, avoiding exclusively rheumatologic or dermatologic interpretations when signs of visceral disease coexist.

Clinical presentations that most often lead to pancreatic imaging

• Persistent epigastric or back pain with weight loss and deterioration in general condition.
• Obstructive jaundice with dark urine and pale stools, especially in the presence of a mass in the pancreatic head.
• Recent-onset diabetes or rapid deterioration of glycemic control without another explanation.
• Steatorrhea and signs of malabsorption consistent with exocrine pancreatic insufficiency.
• Panniculitis and arthralgia associated with hyperlipasemia, suggestive of an enzyme-mediated paraneoplastic syndrome.

Physical examination may reveal jaundice, signs of dehydration or malnutrition, epigastric tenderness and, in advanced stages, hepatomegaly or ascites. Panniculitis lesions, when present, are a particularly valuable diagnostic clue. Overall, clinical findings alone cannot establish the histologic type, but they may indicate the need for prompt histologic confirmation and complete characterization, especially in patients with a paraneoplastic syndrome or suspected metastatic disease.

The diagnostic pathway for pancreatic acinar cell carcinoma begins with suspicion of a pancreatic neoplasm and proceeds through a sequence designed to define location, resectability, histologic type and biological profile. Initial assessment includes a targeted history, physical examination and laboratory testing for cholestasis, liver function, blood glucose and possible signs of malabsorption. Conventional tumor markers used for ductal carcinoma may be useful in the overall assessment but are not specific for acinar histology and cannot replace histologic confirmation.

The first-line imaging examination when clinical suspicion is well founded is pancreatic CT with intravenous contrast and a dedicated protocol, which assesses the mass, vascular relationships and metastases. MRI with cholangiopancreatography may be particularly useful for characterizing lesions that are isoattenuating on CT, evaluating the ducts and better defining necrotic-hemorrhagic or cystic components that may occur. Images must be interpreted in terms of resectability, with attention to involvement of the celiac axis, superior mesenteric artery and portal vein because these findings directly guide the therapeutic strategy.

Definitive confirmation requires an adequate specimen. Endoscopic ultrasonography with fine-needle aspiration or core biopsy is often the procedure of choice for obtaining representative tissue and permits sampling of suspicious lymph nodes. Percutaneous biopsy may be considered when accessible metastases are present or when the endoscopic approach is not feasible. Histologic diagnosis must be supplemented by immunohistochemistry directed at acinar differentiation, using enzyme markers and differential panels to exclude neuroendocrine neoplasms, poorly differentiated carcinomas and mixed tumors.

According to oncology guidelines for pancreatic tumors, correct diagnosis and treatment planning require integration of imaging with histologic definition whenever this information changes management, particularly in locally advanced or metastatic disease and before systemic therapy. Characterization of acinar histology is clinically relevant in this context because it may influence chemotherapy selection and the indication for molecular profiling in advanced disease.

Essential elements for a reliable diagnosis of pancreatic acinar cell carcinoma

• Dedicated pancreatic imaging defining location, local extent and the presence of metastases.
• Histologic confirmation on an adequate specimen, preferably obtained under endoscopic ultrasound guidance.
• Immunohistochemical demonstration of acinar differentiation with appropriate enzyme markers.
• Systematic differential assessment against neuroendocrine tumors, poorly differentiated carcinomas and mixed neoplasms.
• Molecular profiling in advanced or high-risk disease to identify actionable alterations or DNA-repair defects.

Complete radiologic staging includes chest CT and careful assessment of the liver and peritoneum because liver metastases are frequent in advanced disease. In selected cases, 18F-FDG PET may help define disease extent and identify sites suitable for biopsy, although it does not replace dedicated CT for vascular assessment. In patients with obstructive jaundice, endoscopic biliary stenting may be required for clinical stabilization and to allow systemic or surgical treatment to proceed safely.

In summary, diagnosis rests on dedicated pancreatic imaging, histologic confirmation with immunohistochemistry directed at acinar lineage, and definition of disease extent, integrating molecular profiling when disease is advanced or when it may affect treatment selection.

The staging of pancreatic acinar cell carcinoma, in the absence of a universally accepted histology-specific system, is performed in clinical practice using the TNM system for carcinomas of the exocrine pancreas. This approach standardizes communication of disease extent and guides decisions on resectability and treatment, while recognizing that its natural history may differ from that of ductal carcinoma. Staging should be based on high-quality imaging and, when available, pathologic assessment after resection.

A central point is assessment of local extent in relation to major vessels, because the T category includes both size criteria and invasion of major arterial structures, which determine resectability and strategy. Nodal status is expressed by N categories based on the number of metastatic lymph nodes, whereas distant metastases define the M category. In addition to stratifying prognosis, this structure guides the choice among upfront surgery, neoadjuvant strategies and palliative systemic treatment.

TNM categories for carcinoma of the exocrine pancreas (AJCC/UICC 8th edition)

• Tis: carcinoma in situ or high-grade intraepithelial neoplasia confined to the epithelium (Tis).
• T1: tumor confined to the pancreas, measuring 2 cm or less in greatest dimension (T1), with size-based subcategories when reported by pathology.
• T2: tumor confined to the pancreas, measuring more than 2 cm and no more than 4 cm in greatest dimension (T2).
• T3: tumor confined to the pancreas, measuring more than 4 cm in greatest dimension (T3).
• T4: tumor involving the superior mesenteric artery, celiac axis or common hepatic artery, regardless of size (T4).
• N0: no regional lymph-node metastasis (N0).
• N1: metastases in 1-3 regional lymph nodes (N1).
• N2: metastases in 4 or more regional lymph nodes (N2).
• M0: no distant metastases (M0).
• M1: distant metastases present (M1).

Stage groups for carcinoma of the exocrine pancreas (AJCC/UICC 8th edition)

• Stage 0: in situ disease confined to the epithelium, with no regional lymph-node metastases (N0) and no distant metastases (M0), classified as Tis.
• Stage IA: tumor confined to the pancreas measuring up to 2 cm (T1), with no metastatic lymph nodes (N0) and no distant metastases (M0).
• Stage IB: tumor confined to the pancreas measuring more than 2 cm and up to 4 cm (T2), with no metastatic lymph nodes (N0) and no distant metastases (M0).
• Stage IIA: tumor confined to the pancreas measuring more than 4 cm (T3), with no metastatic lymph nodes (N0) and no distant metastases (M0).
• Stage IIB: tumor confined to the pancreas, of any size category T1, T2 or T3, with metastases in 1-3 regional lymph nodes (N1) and no distant metastases (M0).
• Stage III: tumor confined to the pancreas, of any size category T1, T2 or T3, with metastases in 4 or more regional lymph nodes (N2) and no distant metastases (M0), or a tumor involving major arteries (T4) with any nodal status (N) and no distant metastases (M0).
• Stage IV: distant metastases present (M1), regardless of local extent (T) and nodal status (N).

The prognosis of acinar cell carcinoma is heterogeneous. On average it may be more favorable than that of ductal carcinoma in selected populations, especially when disease is resectable, but it remains an aggressive neoplasm with a substantial risk of recurrence. Prognostic determinants include stage at diagnosis, completeness of resection, nodal status, liver or peritoneal metastases and response to systemic therapy. Clinical factors such as performance status and nutritional status have major practical importance because they affect access to intensive treatment and treatment continuity.

Molecular biology may indirectly modify prognosis by providing access to targeted therapies or more effective chemotherapy strategies in subgroups. Profiles consistent with DNA-repair defects or actionable fusions may translate into additional treatment options, whereas mixed tumors with ductal or neuroendocrine components may have a more complex course and require individualized treatment choices. Overall, accurate stage description and early integration of molecular profiling in advanced disease are key to a clinically useful prognostic assessment.

Treatment of pancreatic acinar cell carcinoma is based on a multimodal approach tailored to stage, resectability, general condition and biological profile. The rarity of this entity limits the availability of specific regimens validated in randomized trials, so many decisions rely on retrospective evidence, multicenter series and principles shared with exocrine pancreatic tumors, integrated with emerging data on the sensitivity of acinar cell carcinoma to particular chemotherapy regimens and opportunities for targeted treatment in selected subgroups.

In localized and resectable disease, surgery is the cornerstone of curative-intent treatment. The procedure depends on tumor location, with pancreaticoduodenectomy for tumors of the head and distal pancreatectomy for body-tail lesions, adding splenectomy when indicated. Resection should aim for negative margins and include adequate lymphadenectomy for accurate staging, because nodal status affects prognosis and adjuvant decisions. In patients with jaundice or malnutrition, preoperative stabilization and nutritional support are critical to reduce morbidity.

Systemic therapy is central in locally advanced or metastatic disease and may also be considered after resection in high-risk settings following multidisciplinary assessment. In patients fit for intensive regimens, fluoropyrimidine-, irinotecan- and platinum-based combinations such as FOLFIRINOX or variants are frequently used, with meaningful responses reported in a subset of cases. Alternatives include gemcitabine-platinum combinations or other regimens selected according to performance status, comorbidities and treatment goals.

A distinctive element is the importance of molecular profiling in advanced disease. DNA-repair alterations may support the use of platinum and, in selected and well-characterized settings, targeted strategies. MAPK-pathway fusions or alterations and other potentially actionable abnormalities may permit targeted therapy in selected patients, preferably at centers with access to precision-oncology pathways and clinical trials. Radiotherapy may be used in selected settings for local control, pain or consolidation in locally advanced disease, with case-by-case decisions based on objectives and toxicity risk.

Treatment objectives and options according to clinical setting

• Localized disease: surgical resection with curative intent and multidisciplinary assessment of adjuvant therapy according to stage, margins and clinical risk.
• Locally advanced disease: systemic therapy as the main strategy, with periodic reassessment of resectability and integration of radiotherapy in selected cases.
• Metastatic disease: systemic chemotherapy aimed at disease and symptom control, favoring effective regimens in suitable subgroups and integrating targeted therapies when actionable alterations are present.
• Enzyme-mediated paraneoplastic syndromes: control of the neoplasm as causal treatment, together with symptomatic management of panniculitis, pain and metabolic complications.

Supportive management is an integral part of treatment. Pain control, correction of cholestasis and malnutrition, pancreatic enzyme replacement for exocrine insufficiency and diabetes management improve treatment tolerance and quality of life. In advanced disease, early integration of palliative care and clinical nutrition facilitates continuity of treatment and reduces symptom burden, particularly when sarcopenia, fatigue and paraneoplastic complications coexist.

Follow-up and post-treatment surveillance for pancreatic acinar cell carcinoma should be structured but individualized because dedicated evidence is limited and the clinical trajectory may vary according to stage and treatment received. After curative-intent resection, recurrence risk is clinically significant, making surveillance appropriate through an integration of clinical assessment, laboratory monitoring focused on liver function, nutrition and metabolism, and periodic imaging to detect locoregional or metastatic recurrence at a potentially treatable stage.

During the first years after surgery, surveillance focuses on symptoms suggestive of recurrence, weight loss, abdominal pain and signs of pancreatic insufficiency. Nutritional status should be assessed systematically because pancreatic resection and systemic treatments can cause malabsorption, sarcopenia and micronutrient deficiencies. Pancreatic enzyme replacement and dietary education can reduce diarrhea, steatorrhea and weight loss, directly improving quality of life and the ability to continue any required oncologic therapy.

Imaging with contrast-enhanced CT or MRI is used for surveillance, with frequency and duration tailored to risk and clinical condition. In patients treated for advanced disease, follow-up centers on response assessment, early detection of toxicity and dynamic adjustment of the treatment strategy. Molecular reassessment may be considered at progression, particularly when targeted options or clinical trials are available.

Overall, effective surveillance requires continuity of care, active management of malnutrition and pancreatic dysfunction, monitoring of metabolic complications and an imaging schedule consistent with disease stage and treatment goals.

Long-term quality-of-life considerations in pancreatic acinar cell carcinoma depend on the interaction among surgical outcomes, the impact of chemotherapy and the functional consequences of pancreatic insufficiency. Even in patients who achieve disease control or cure, dietary adjustments, management of diarrhea and steatorrhea and diabetes monitoring may become permanent aspects of daily life, affecting energy, social life and work capacity.

After pancreatic resection, quality of life is often affected by exocrine pancreatic insufficiency and changes in gastrointestinal transit. Correct use of pancreatic enzymes, individualized diet and ongoing dietetic support are high-impact interventions because they reduce symptoms, improve absorption and promote weight recovery. Deficiencies of fat-soluble vitamins and micronutrients require monitoring and targeted supplementation, particularly in patients with persistent weight loss or reduced intake.

Systemic therapies may leave persistent effects such as peripheral neuropathy, chronic fatigue and mood changes. In patients who have received intensive regimens, functional rehabilitation and adapted physical activity help restore performance and reduce sarcopenia. Pain, which is often multifactorial, requires an integrated approach including pharmacologic therapy, supportive interventions and pain-specialist consultation when indicated.

The psychological dimension is influenced by the perceived severity of a pancreatic cancer diagnosis and fear of recurrence, which may persist even in disease-free patients. Psycho-oncologic support, clear communication about the rationale for follow-up and multidisciplinary integration promote adjustment and reduce the effects of uncertainty and stress. Overall, preserving quality of life requires continuous care that combines oncologic control with correction of pancreatic dysfunction, nutritional support and management of late treatment effects.

Complications of pancreatic acinar cell carcinoma arise from local progression, systemic dissemination and treatment effects. Local progression may cause severe pain, biliary obstruction with cholangitis, duodenal obstruction and malabsorption, with rapid deterioration in nutritional status. Metastatic disease, often involving the liver, may cause hepatic failure, ascites and functional decline, whereas peritoneal involvement may lead to subacute obstruction and cachexia.

A distinctive complication, when present, is hyperlipasemia syndrome with panniculitis and arthralgia caused by tumor enzyme secretion. This syndrome may cause pain, functional limitation and ulcerated skin lesions, and tends to improve when the disease responds to systemic treatment. Oncologic control is therefore the principal causal measure, combined with multidisciplinary symptomatic management.

Surgical complications include pancreatic fistula, delayed gastric emptying, infections and postoperative bleeding, with higher risk in malnourished or jaundiced patients. In the long term, exocrine and endocrine pancreatic insufficiency are common and clinically important outcomes requiring pancreatic enzyme replacement, glycemic monitoring and correction of nutritional deficiencies. Endoscopic biliary procedures may also be complicated by post-ERCP pancreatitis, cholangitis or stent migration, requiring close clinical surveillance.

• Chemotherapy toxicity: neutropenia, infections, mucositis, diarrhea, nausea and peripheral neuropathy, requiring prevention and early management.
• Metabolic complications: post-resection diabetes or worsening of pre-existing diabetes, hypoglycemia and glycemic instability during systemic treatment.
• Nutritional complications: steatorrhea, weight loss, sarcopenia and fat-soluble vitamin deficiencies, affecting performance status and treatment tolerance.

Prevention and management of complications rely on early nutritional support, optimization of biliary and pancreatic function, targeted laboratory monitoring and multidisciplinary integration. In patients with advanced disease, early integration of palliative care permits more effective symptom control, fewer unplanned hospital admissions and improved continuity of care.