Rectal Melanoma with Solitary Pancreatic Metastasis

A 45-year-old asymptomatic female diagnosed with rectal melanoma 1 year back, on immunotherapy, was referred for evaluation of a pancreatic head lesion of size 3.18 × 3.25 cm, detected on routine follow-up ¹⁸F-fluorodeoxyglucose positron emission tomography with maximum standardized uptake value 15.63 ([Fig. 1]). Endoscopic ultrasound (EUS) assessment revealed a well-defined hypoechoic mass lesion in the head of the pancreas, closely abutting the main portal vein ([Fig. 2]). The lesion was stiff on EUS elastography and showed hyperenhancement with rapid washout on intravenous contrast ([Fig. 3]). Histopathology of tissue specimen acquired under EUS guidance revealed many singly scattered tumor cells with round to oval nuclei with opened up chromatin admixed with pancreatic acinar cells, consistent with the diagnosis of metastatic melanoma ([Fig. 4]).

Fig. 1 ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET): FDG-avid lesion in the head of the pancreas.

Fig. 2 Endoscopic ultrasound (EUS): Well-defined hypoechoic lesion in the head of the pancreas.

Fig. 3 Contrast-enhanced endoscopic ultrasound (EUS): The pancreatic lesion is hyperenhancing.

Fig. 4 Microphotograph showing large atypical cells with opened up chromatin and prominent nucleoli admixed with pancreatic acinar cells (May–Grunwald Giemsa stain ×400).

Practical Implications for Endoscopists

• Consider metastasis in pancreatic lesions with known primary malignancy, as they represent 2% of all pancreatic malignancies.[1]

• Most common primary tumor sites causing metastasis to pancreas are renal cell carcinoma, ovary, colon, and melanoma.[2]

• Most common sites of metastasis for melanoma are the lymph nodes, lung, liver, central nervous system, and bone. Gastrointestinal and pancreatic metastases are rare.[3]

• Use elastography and contrast-enhanced EUS to support malignancy suspicion along with EUS-guided fine-needle aspiration/fine-needle biopsy with cytopathology and immunohistochemistry for definitive diagnosis.

• EUS remains a cornerstone for evaluation, particularly in characterizing lesions and guiding tissue acquisition safely in vascularly complex areas.

 

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Conflict of Interest

None declared.

• References

• 1 Zerbi A, Pecorelli N. Pancreatic metastases: an increasing clinical entity. World J Gastrointest Surg 2010; 2 (08) 255-259
• 2 Konstantinidis IT, Dursun A, Zheng H. et al. Metastatic tumors in the pancreas in the modern era. J Am Coll Surg 2010; 211 (06) 749-753
• 3 Balch CM, Gershenwald JE, Soong SJ. et al. Final version of 2009 AJCC melanoma staging and classification. J Clin Oncol 2009; 27 (36) 6199-6206

Publication History

Article published online:
28 July 2025