The patient underwent to a partial colectomy:

MICROSCOPIC DESCRIPTION: Sections from the sigmoid show an ulcerated moderately differentiated adenocarcinoma composed of irregular glands with a complex cribriform architecture, many with central necrosis and associated calcification. Malignant glands focally infiltrate the pericolic fat and extend beyond the muscularis propria to within 5mm of the serosal surface. The malignant cells have pleomorphic vesicular nuclei and prominent nucleoli. Mitotic figures are frequent. The stroma is desmoplastic and the tumor is associated with a moderate to heavy lymphocytic and neutrophilic infiltrate. Perineural and lymphovascular invasion are not identified. One of twenty eight lymph nodes is involved by metastatic tumor.

DIAGNOSIS: Sigmoid colon: * Moderately differentiated adenocarcinoma, invading through muscularis propria into pericolic tissue (pT3) - Obstructing circumferential tumor 60mm in length - Clear of serosa - Well clear of margins - No perineural or lymphovascular invasion - 1 our of 28 lymph nodes involved by tumor (1/28). - pT3 pN1c AJCC stage IIIB.

IMMUNOHISTOCHEMISTRY Mismatch repair proteins MLH1 POSITIVE PMS2 POSITIVE MSH2 POSITIVE MSH6 POSITIVE There is normal expression of mismatch repair proteins in tumor cells, indicating that the tumor is mismatch repair proficient (microsatellite stable, MSS). BRAF V600E NEGATIVE