Amplification and overexpression of PSCA at 8q24 in invasive micropapillary carcinoma of breast.

Purpose: Invasive micropapillary carcinoma (IMPC) of the breast has distinct histological features and molecular genetic profiles. Gains/amplifications of 8q24 are found associated with IMPC. Although the prostate stem cell antigen (PSCA) gene is located at chromosome 8q24, and found over-expressed in prior studies, its prognostic values and biological significance in IMPC have not been well studied.

Methods: Fluorescence in situ hybridization (FISH) was used to assess the frequencies of PSCA copy number gains in IMPC, invasive ductal carcinoma of no special type (IDC-NST), and invasive lobular carcinoma (ILC) samples. The protein expression levels of PSCA were examined in 56 IMPC, 72 IDC-NST, and 56 ILC samples using immunohistochemical analysis.

Results: PSCA gene amplification was detected in 45.2% (14/31) of the IMPC, 28.1% (9/32) of the IDC-NST, and none (0/25) of the ILC. PSCA protein expression was observed in 58.9% (33/56), 40.3% (29/72), and 3.6% (2/56) of IMPC, IDC-NST, and ILC samples, respectively. The concordant rate of the immunohistochemistry and FISH data was 85.2%. PSCA gene amplification highly correlated with its protein overexpression (rs = 0.687, P < 0.001), suggesting that gene amplification is an important mechanism involved in PSCA overexpression. Our univariate analysis showed that the patients with PSCA-positive IMPC had a decreased disease-free survival (DFS) compared to PSCA-negative IMPC patients (P = 0.003). Our multivariate analysis confirmed the worse DFS in PSCA-positive IMPC patients (P = 0.022).

Conclusions: Our results indicate that PSCA may be an attractive target in the 8q24 amplicon and that it may serve as a molecular marker of metastasis and recurrence in IMPC. The differential expression of PSCA may be associated with cell adhesion. Detection of PSCA protein and gene amplification may help manage and predict the prognosis of IMPC patients.