Colorectal medullary carcinoma: heterogeneous presentations of a rare clinico-pathological entity. Report of two cases.

Colorectal medullary carcinoma (CMC) is a rare subset of minimally differentiated carcinomas. CMC tend to be right-sided and present at an advanced stage. Despite this, distant metastases are rare at presentation. The liver and the regional lymph nodes represent the most common sites of metastases. Most of the time, CMCs exhibit mismatch repair deficiency and a strong association with high-level microsatellite instability. There is no conspicuous data regarding treatment strategies and short-term outcomes. CMC is supposed to be related to better prognosis compared to poorly-differentiated and undifferentiated colonic adenocarcinomas, but reports are controversial.This lesion, with heterogeneous presentations and unclear prognostic significance, may be unfamiliar to histopathologists and can lead to diagnostic uncertainty and overtreatments.Our aim is to renew the attention to this rare histological subtype through the report of two cases.