PLC-gamma-1 phosphorylation status is prognostic of metastatic risk in patients with early-stage Luminal-A and -B breast cancer subtypes

Abstract

Background: Phospholipase Cγ1 (PLCγ1) is highly expressed in human tumours. Our previous studies reported that both stable and inducible PLCγ1 down-regulation can inhibit formation of breast-cancer-derived experimental lung metastasis. Further, high expression of PLCγ1 and its constitutively activated forms (i.e., PLCγ1-pY1253, PLCγ1-pY783) is associated with worse clinical outcome in terms of incidence of distant metastases, but not of local relapse in T1-T2, N0 breast cancer patients.

Methods: In the present retrospective study, we analysed the prognostic role of PLCγ1 in early breast cancer patients stratified according to the St. Gallen criteria and to their menopausal status. PLCγ1-pY1253 and PLCγ1-pY783 protein expression levels were determined by immunohistochemistry on tissue microarrays, and were correlated with patients' clinical data, using univariate and multivariate statistical analyses.

Results: In our series, the prognostic value of PLCγ1 overexpression was restricted to Luminal type tumours. From multivariate analyses, pY1253-PLCγ1^High was an independent prognostic factor only in postmenopausal patients with Luminal-B tumours (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.1-5.3; P = 0.034). Conversely, PLCγ1-pY783^High was a remarkably strong risk factor (HR, 20.1; 95% CI, 2.2-178.4; P = 0.003) for pre/perimenopausal patients with Luminal-A tumours.

Conclusions: PLCγ1 overexpression is a strong predictive surrogate marker of development of metastases in early Luminal-A and -B breast cancer patients, being able to discriminate patients with high and low risk of metastases. Therefore, targeting the PLCγ1 pathway can be considered of potential benefit for prevention of metastatic disease.

Keywords: Breast cancer; Luminal subtypes; Menopausal status; Phospholipase Cγ1; Prognosis.

Fig. 1

PLCγ1-pY1253 and PLCγ1-pY783 immunostaining: examples of high (upper panel) and low (lower panel) expression in Luminal-A and Luminal-B breast cancer subtypes. Expression of PLCγ1 phosphorylated forms is confined to tumor cell nuclei

Fig. 2

Kaplan-Meier plots in the Luminal-A subtype. Kaplan-Meier estimates of DFS, LRFS and DRFS in patients with Luminal-A tumours (n = 156), according to high (solid green lines) and low (dashed blue lines) expression of PLCγ1, PLCγ1-pY1253 and PLCγ1-pY783. In this cohort, the patients showed distant relapse in 6% (5/91) PLCγ1^Low and 14% (9/65) PLCγ1^High, in 4% (4/90) PLCγ1-pY1253^Low and 15% (10/66) PLCγ1-pY1253^High, and in 3% (4/119) PLCγ1-pY783^Low and 27% (10/37) PLCγ1-pY783^High

Fig. 3

Kaplan-Meier plots in Luminal-B subtype. Kaplan-Meier estimates of DFS, LRFS and DRFS in patients with Luminal-B tumours (n = 176), according to high (solid green lines) and low (dashed blue lines) expression of PLCγ1, PLCγ1-pY1253 and PLCγ1-pY783. In this cohort, the patients showed distant relapse in 15% (12/81) PLCγ1^Low and 24% (23/95) PLCγ1^High, in 13% (13/100) PLCγ1-pY1253^Low and 29% (22/76) PLCγ1-pY1253^High, and in 19% (27/140) PLCγ1-pY783^Low and 22% (8/36) PLCγ1-pY783^High

Fig. 4

Kaplan-Meier plots in Luminal-A and Luminal-B subtypes. Kaplan-Meier estimates of DRFS in patients with Luminal-A and Luminal-B tumours according to menopausal status. In Luminal-A tumours, the patients with postmenopausal status showed distant relapse in 5% (3/62) PLCγ1-pY1253^Low and 11% (5/44) PLCγ1-pY1253^High, and in 5% (4/82) PLCγ1-pY783^Low and 17% (4/24) PLCγ1-pY783^High, and the patients with premenopausal status showed distant relapse in 4% (1/28) PLCγ1-pY1253^Low and 23% (5/22) PLCγ1-pY1253^High, and in 0% (0/37) PLCγ1-pY783^Low and 46% (6/13) PLCγ1-pY783^High. In Luminal-B tumours, the patients with postmenopausal status showed distant relapse in 12% (9/76) PLCγ1-pY1253^Low and 29% (18/63) PLCγ1-pY1253^High, and in 20% (22/109) PLCγ1-pY783^Low and 17% (5/30) PLCγ1-pY783^High, and the patients with premenopausal status showed distant relapse in 17% (4/24) PLCγ1-pY1253^Low and 31% (4/13) PLCγ1-pY1253^High, and in 16% (5/31) PLCγ1-pY783^Low and 50% (3/6) PLCγ1-pY783^High

Fig. 5

DRFS estimates in Luminal-A premenopausal patients treated with hormonal therapy alone (left) and chemotherapy plus hormonal therapy (right). In this cohort, a distant relapse occurred in 0% (0/12) PLCγ1-pY783^Low and 66% (2/3) PLCγ1-pY783^High of patients treated with hormonal therapy (n = 15), and in 0% (0/23) PLCγ1-pY783^Low and 40% (4/10) PLCγ1-pY783^High of patients treated with chemotherapy plus hormonal therapy (n = 33). The solid green line and dashed blue line represent high and low expression of PLCγ1-pY783, respectively