Microsatellite Instability in Medullary Carcinoma of the Colon

Abstract

Medullary carcinoma (MC) of the large intestine is a relatively new histological type of adenocarcinoma characterized by poor glandular differentiation and an intraepithelial lymphocytic infiltrate. MC can be associated to a defective mechanism for DNA mismatch repair, caused by the so-called microsatellite instability (MSI). We present the case of a 44 years old Caucasian woman, who referred to the Emergency Room with symptoms mimicking an acute appendicitis. Computed tomography and colonoscopy demonstrated an ulcerated and stenotic lesion of the caecum without signs of metastasis and peritoneal carcinosis. Patient underwent a laparoscopic right colectomy. The final pathologic findings provided the diagnosis of medullary carcinoma with MSI. Patient then underwent adjuvant chemotherapy according to the FOLFOX-4 protocol (association of 5-Fluorouracil, Leucovorin, and Oxaliplatin) for twelve cycles. At two-years follow-up, patient is disease free. MC in association with MSI is a non-frequent tumor of the colon characterized by a better prognosis compared to other types of poorly differentiated adenocarcinoma. In the observed case, 24 months after the surgical operation, the patient is in good health and there is no evidence of metastasis or relapse.

Keywords: colorectal carcinom; medullary carcinoma; microsatellite instability.

Figure 1.

Hematoxylin and Eosin stains of Medullary carcinoma (100×).

Figure 2.

Medullary carcinoma showing negative staining with MLH-1 (A) and CDX-2 (B). Medullary carcinoma showing positive nuclear and cytoplasmic staining with Calretinin (C). Proliferation index assessed with Ki67/MIB-1 (D) (×200). CK AE1/AE3 was focally positive (E) (×200).