Carcinoma of unknown primary with a "gastrointestinal profile" is an emerging, favorable entity. Distinguishing this entity is of increasing significance given the progress in the treatment of colorectal cancer.

74 carcinoma of unknown primary (CUP) patients with CDX2+ tumors were chosen from the databases at M.D. Anderson and Sarah Cannon Cancer Centers between 2004 and 2010. Data on clinical and pathological characteristics including therapy and survival were recorded.

20 patients had ascites on presentation; the predominant sites of metastases included liver (30 %), carcinomatosis (50 %), and nodes (51 %). Based on immunohistochemistry, 2 cohorts were created: Cohort 1-"consistent with lower GI profile" included 34 patients [CDX-2+, CK20+, CK7-] and Cohort 2-"probable lower GI profile" included 40 patients [CDX2+, irrespective of CK7/CK20 status]. Excluding 6 outliers, Cohorts 1 and 2 had 32 and 36 patients, respectively; their median survivals were 37 and 21 months, respectively. On multivariate Cox regression analysis, only liver metastases were found to negatively influence survival.

Our retrospective study provides encouraging indications that CUP patients with gastrointestinal profiles benefit from site-specific therapy. We recommend all CUP patients, especially those with abdominal nodes, isolated carcinomatosis or liver metastases, to undergo optimal immunohistochemistry (IHC) to check for a gastrointestinal profile of CUP.