[637] "In Situ" Growth of Metastatic Tumors to the Gastrointestinal Tract: A Potential Mimic of Primary Neoplasia

JS Estrella, A Rashid, SC Abraham. MD Anderson Cancer Center, Houston

Background: It can be difficult to distinguish primary from metastatic neoplasms to the gastrointestinal (GI) tract, particularly in the small bowel where metastatic tumors outnumber primaries. The presence of an adenomatous precursor is usually taken as strong evidence for primary neoplasia. Gross configuration of the tumor and regional lymph node involvement are also features commonly used in this distinction.
Design: We studied GI resections from 1987-2009 that were reported to show mucosal involvement by metastatic carcinoma. Gross descriptions and histologic sections were evaluated for the following: 1) "in situ" growth (i.e., growth within the basement membrane of villi/crypts), 2) resemblance to a precursor/adenoma, 3) maturation of tumor cells toward the lumen (i.e, better differentiated tumor within mucosa and less differentiated tumor - including presence of tumor budding - in the wall), 4) gross configuration of the metastasis, and 5) lymph node involvement in the metastatic site.
Results: Detailed results are presented in Table 1. The study population comprised 99 resections from small bowel (n=75), colorectum (n=14) or both (n=10). Many (74%) metastatic carcinomas lacked a classic serosal-based configuration and showed lymph node involvement in the metastatic site (64%). Carcinomas originating from the GI tract were significantly more likely to show in situ growth (p<0.0001), resemblance to a precursor (p<0.0001), and maturation toward the mucosa (p<0.0001). In 5 cases (3 GI and 2 GYN origin), metastatic tumors were initially interpreted as new primaries by the pathologist (n=4) or radiologist (n=1).
Conclusions: Metastatic carcinomas involving the intestinal mucosa can exhibit histologic features mimicking second primaries, particularly when they originate from the GI or GYN tract. Presence of an apparent adenoma cannot be taken as prima facie evidence of a primary neoplasm.

Table 1
Primary siteIn situ growthPrecursor resemblanceMaturation toward mucosaNon-serosal based configurationLymph node involvement
GI tract (n=56)34 (61%)26 (46%)28 (50%)45 (80%)11 of 22 (50%)
GYN tract (n-28)6 (21%)2 (7%)1 (4%)15 (54%)14 of 19 (74%)
Lung (n=7)2 (29%)0 (0%)0 (0%)6 (86%)4 of 5 (80%)
GU tract (n=5)0 (0%)0 (0%)0 (0%)5 (100%)1 of 2 (50%)
Head & neck (n=2)0 (0%)0 (0%)0 (0%)1 (50%)2 of 2 (100%)
Breast (n=1)1 (100%)0 (0%)0 (0%)1 (100%)Not sampled



Category: Gastrointestinal

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 68, Tuesday Afternoon

 

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