Contributed by Dane C. Olevian, MD and Reetesh K. Pai, MD
The patient was a 71 year old male with a history of diabetes and coronary artery disease who presented to the emergency department with recent progressive constipation, black stools, and cramping abdominal pain. A CT scan revealed an obstruction in the transverse colon suspicious for a mass, but no overt evidence of metastatic disease was identified. A colonoscopy was then performed, which confirmed the radiologic impression. The patient ultimately underwent a right hemicolectomy and the resection specimen was submitted for pathologic evaluation.
Received is a right partial colectomy specimen consisting of a 7.2 cm length of terminal ileum and a 34.7 cm length of portion of cecum and ascending colon. A 4.2 x 3.5 cm circumferentially stenosing mass is present in the ascending colon, with a tan-red, granular, and focally necrotic appearance. The mass invades through the colonic wall into the serosa and surrounding adipose tissue. Multiple tan sessile polyps are also identified, ranging in size from 0.3 cm to 2.7 cm in diameter. One 2.5 cm tan-white firm nodule is present in the omentum and numerous lymph nodes are identified throughout the adipose tissue. (Gross images are not available).
The normal colonic architecture is largely effaced by a deeply infiltrating lesion that extends from the epithelium through the muscularis propria and penetrates the visceral peritoneum (images 1 and 2). The tumor demonstrates a biphasic population of neoplastic cells amongst a desmoplastic stroma. Approximately 70% of the tumor volume is composed of intermediate to large-sized neuroendocrine-type cells with generally round nuclei that have finely stippled chromatin and occasionally prominent nucleoli (image 3). Occasional nuclear molding is evident. The cells have scant to moderate amounts of eosinophilic cytoplasm and are frequently arranged in densely packed small nests and clusters, as well as in a rosette-like pattern (image 4).
Approximately 30% of the tumor is composed of signet ring-type cells with large central cytoplasmic mucin vacuoles and thin, eccentrically-placed nuclei (image 5). In some areas, signet ring cells are closely associated with tight clusters of neuroendocrine-type cells (image 6). In other areas, both cell components float freely in large pools of extracellular mucin (image 7). Mitotic figures are readily identified (30 per 10 HPF). Widespread perineural invasion (images 8 and 9) and lymphovascular invasion (image 10) is present. Metastatic signet ring and neuroendocrine components are identified in 6 of 23 lymph nodes examined (image 11). A focus of carcinoma is also found in the omentum (image 12). The uninvolved colon features numerous sessile serrated adenomas and an appendix with a mild acute epithelial inflammatory infiltrate (not shown).
The tumor is diffusely positive for synaptophysin (image 13), including cells with neuroendocrine morphology (image 14) and signet ring morphology (image 15). The tumor also shows partial immunoreactivity to chromogranin (image 16). The cells with neuroendocrine and signet ring morphology are both focally positive for CDX2 (image 17), CK7 (image 18), and CK20 (image 19). Immunohistochemistry reveals a Ki-67 proliferative index of 80% (image 20).