The patient proceeded to subtotal colectomy.

Macroscopic description "Bowel": A subtotal colectomy specimen including a segment of large bowel 625mm long, up to 60mm in diameter. Received separately is a short segment of bowel 15mm long and 20mm in diameter. The attached appendix is 50mm long and 5mm in diameter. The pericolic adipose tissue is up to 70mm wide and 20mm thick. At 520mm from the proximal resection and 70mm from the distal resection margin there is an obstructing, indurated and ulcerated tumor measuring 25mm in length and involving the bowel wall lumen circumferentially. At this level the serosal surface is indurated and puckered. The remaining bowel mucosa is unremarkable with no other focal lesions identified. The mesoappendix is 10mm wide. No focal lesions are seen on sectioning the appendix. The proximal resection margin of the colectomy specimen is inked blue and the distal resection margin is inked black. The tumor is 20mm deep, infiltrating the entire bowel wall and extending into the pericolic adipose tissue and abutting the serosal surface. Several lymph nodes are found and processed.

Microscopic description: In this large bowel wall there is a moderately differentiated adenocarcinoma composed of irregular glands lined by atypical cells with pleomorphic nuclei, prominent nucleoli and frequent mitoses. There is significant mucinous component representing approximately 30% of tumor volume. This comprises pools of mucin with small stranded islands of atypical tumor cells. The carcinoma infiltrates the entire bowel wall also extending to the pericolic adipose tissue. Focally tumor nests and atypical glands are abutting the serosal surface (pT4a). There is a tumor deposit which appears to replace a lymph node. Of the remaining 18 lymph nodes, one includes a small focus of carcinoma, 17 are free of metastatic deposits. Both longitudinal resection margins are well clear. No perineural or lymphovascular space invasion is seen. The lumen of the appendix is fibrosed but otherwise the appendix is unremarkable. The sections from the separate segment of large bowel wall are histologically unremarkable.

Diagnosis: Subtotal colectomy: Moderately differentiated adenocarcinoma NOS of the splenic flexure, extending to the serosal surface, with 2 out of 19 lymph nodes involved. AJCC stage IIIB (TNM pT4a N1b MX)