| Summary: | Primary colorectal signet ring cell carcinoma (SRCC) is a rare but distinctive type of mucin-producing adenocarcinoma of the large intestine with still controversial clinicopathological features and prognosis. We encountered primary colonic SRCC in a 51-year-old Japanese man with extensive bone metastasis ultimately leading to carcinocythemia before the initiation of chemotherapy and surgical intervention. Three days before death, besides progressive disseminated intravascular coagulation that had been present on admission, hematological examination showed sudden leukocytosis with nonhematopoietic cells that subsequently turned out to be signet ring cells (SRCs). Carcinocythemia, the presence of circulating cancer cells in peripheral blood, is considered to be a rare but an ominous phenomenon occurring in the advanced stage of certain types of cancers, particularly mammary lobular carcinoma. It can be assumed that carcinoma cells lacking intercellular cohesiveness and polarized cell membrane organization, including SRCs as well as lobular carcinoma cells, can readily get access to the peripheral circulation; however, to our knowledge, this is the first report of primary colorectal SRCC that presented carcinocythemia. Extensive bone metastatic sites, in the present case, may have functioned as a reservoir of circulating SRCs.
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