Aberrant Partial Chromosomal Instability With Chemotherapeutically Resistant Metachronous Colorectal Cancer Following a Synchronous Primary Colorectal Cancer: A Case Report.

The diagnosis of synchronous colorectal cancer (CRC) is crucial as the management, including the extent of surgical resection, depends on it. There have been numerous studies on the clinicopathological features of synchronous CRC; however, only a few studies have discussed synchronous cancer treatment. The guidelines to best manage the synchronous and metachronous CRC are limited, especially the most appropriate surgical treatment and chemotherapy based on mutational analysis of mismatch repair genes and the carcinoma sequence model. We present a rare case of a metachronous CRC with intact nuclear expression of microsatellite instability markers following a synchronous CRC, and it failed to show any significant response to surgical resection and chemoradiotherapy. A 53-year-old female presented in June 2016 with bleeding per rectum for one month, weight loss, and a recent history of altered bowel habits. The per rectal examination revealed a circumferential growth. Colonoscopy and biopsy yielded multiple polyps throughout the colon and invasive adenocarcinoma in the upper and lower one-third of the rectum. The above features were highly suggestive of synchronous CRC. Serologic studies revealed elevated carcinoembryonic antigen (CEA). Excisional biopsy of mesenteric and retroperitoneal lymph nodes during proctocolectomy and end ileostomy was negative for metastasis, including the other metastatic workup preoperatively-eight months post-resection and adjuvant chemotherapy patient developed metachronous CRC. Mutational analysis showed positivity only for