Shc proteins are strong, independent prognostic markers for both node-negative and node-positive primary breast cancer

Abstract

Activated Shc signaling proteins are implicated in many pathways associated with aggressive disease, and many breast cancer cell lines derived from highly aggressive tumors contain high levels of activated, tyrosine phosphorylated (PY)-Shc (the M(r) 46000 and M(r) 52000 isoforms) relative to levels of an inhibitory M(r) 66000 Shc isoform. It was, therefore, hypothesized that high amounts of PY-Shc relative to the M(r) 66000 Shc isoform would serve as a marker for aggressive neoplasms. Semiquantitative immunohistochemical analyses of PY-Shc and p66 Shc were performed on archival primary breast tumor specimens from 116 women, 17 of whom experienced relapse (6.1 years median follow-up of nonrelapsed patients). Consistent with our hypothesis, staining intensities demonstrated that increased amounts of PY-Shc (P = 0.01) and decreased expression of p66-Shc protein (P = 0.028) correlated with disease recurrence. Modeled as the ratio of PY-Shc to p66 Shc, the Shc ratio correlated strongly with nodal status (P = 0.003), tumor stage (P = 0.0025), and disease stage (P = 0.002) and was 2-fold higher in primary tumors of patients who subsequently relapsed (P < 0.001). Univariate Cox proportional hazards analysis of relapse-free survival demonstrated the prognostic value of PY-Shc (P = 0.01), p66 Shc (P = 0.04), and the Shc ratio (P = 0.004) as continuous variables, with a hazard ratio (HR) of 10 (P = 0.007) for the Shc ratio. Shc ratio cut points of <0.35 and >0.65 were identified and independently validated to maximize negative predictive value and positive predictive value. Patients with low Shc ratios (n = 36) had a 0.08 HR of relapse (P = 0.007) compared with patients with high Shc ratios, experiencing an 8-year cumulative 2.9% and 55% relapse hazard, respectively, compared with a 22% relapse hazard in the total cohort. The Shc ratio had similar prognostic value for disease-specific survival. In multivariate models, the Shc ratio, both as a continuous variable and as a cut point-categorized variable, was independent of all measured covariates (including nodal status, tumor stage, disease stage, grade, estrogen receptor status, and adjuvant therapy) and was a stronger prognostic marker than all but nodal status. All relapsed node-positive patients had very high Shc ratios (>0.80; P = 0.006) in their primary tumors. Furthermore, the Shc ratio was a strong, independent prognostic indicator in node-negative patients (79 patients, 10 recurrences), with a HR of 0.086 (P = 0.02) that was independent of clinical markers and adjuvant therapy. Patients with low and high Shc ratios experienced a 3.6% and 64% relapse hazard, respectively, compared with 20% in the total node-negative cohort.