OBJECTIVETo study the clinicopathologic features and immunophenotype of gastrointestinal adenocarcinomas with a micropapillary pattern differentiation (GAMPD).

METHODSSeventy-three cases of GAMPD arising in gastrointestinal tract were retrospectively reviewed. Immunohistochemical study for epithelial membrane antigen (EMA), insulin-like growth factor II mRNA-binding protein-3 (IMP3) and E-cadherin was performed.

RESULTSAmongst the 73 cases studied, the micropapillary pattern accounted for 5% to 70% of the tumor component. It was often seen in a background of moderately differentiated adenocarcinoma. As compared with conventional adenocarcinoma, nodal metastasis was more frequently observed and the TNM tumor stage was statistically higher in GAMPD. The occurrence of micropapillary component in metastatic lymph nodes positively correlated with the proportion of micropapillary pattern in primary lesions. EMA staining on the stroma-facing surface of tumor micropapillae was demonstrated in 52.1% (38/73) of the cases. As compared with EMA-negative GAMPD, EMA-positive GAMPD was more in the stomach (P = 0.018), and with more metastatic lymph nodes (6.6 ± 5.8 vs 3.8 ± 4.7, P = 0.029). The rate of IMP3 expression in EMA-positive GAMPD was 86.8%(33/38), which was higher than that in conventional adenocarcinoma. In contrast, the rate of E-cadherin expression in GAMPD was lower than that in conventional adenocarcinoma.

CONCLUSIONSGAMPD is a distinctive variant of gastrointestinal adenocarcinomas and different from conventional adenocarcinoma in tumor morphology, immunophenotype and biologic behavior. It carries an aggressive clinical course and poor prognostic outcome. Immunohistochemical study for EMA, IMP3 and E-cadherin would be helpful in the diagnosis and prognostic evaluation of GAMPD.