Answer: Tubular adenoma with a metastatic well-differentiated endocrine neoplasm in a node

Histology: Two histologically distinct neoplasms are present, a mucosal lesion in the ampulla, and a separate one in a lymph node. The mucosal lesion is a gland-forming adenoma. The neoplasm in the lymph node forms nests, not lumina, and has the characteristic appearance of a well-differentiated endocrine neoplasm.

Discussion: This in an unusual case in which the patient had surgery for one neoplasm (an adenoma) and was found to have a second, more aggressive but clinically silent neoplasm (a metastatic well-differentiated endocrine neoplasm). Although rare, cases such as this one highlight the importance of keeping an open mind when reviewing a case. It is easy to miss a diffuse lymphoma in a lymph node if all of one’s energies are focused on evaluating the subcapsular sinus for small metastases. Similarly, once a primary neoplasm has been identified it is easy to assume that all metastases have originated from that primary. Taking time to evaluate lymph nodes at low-power and comparing the morphologies of the different lesions identified can help avoid these pitfalls. In this case the fact that the primary was non-invasive, together with immunolabeling with endocrine markers, helped establish the diagnosis of two unrelated neoplasms.