p66 Shc and tyrosine-phosphorylated Shc in primary breast tumors identify patients likely to relapse despite tamoxifen therapy

Abstract

Introduction: Shc adapter proteins are secondary messenger proteins involved in various cellular pathways, including those mediating receptor tyrosine kinase signaling and apoptosis in response to stress. We have previously reported that high levels of tyrosine-phosphorylated Shc (PY-Shc) and low levels of its inhibitory p66 Shc isoform are strongly prognostic for identifying both early node-negative and more advanced, node-positive, primary breast cancers with high risk for recurrence. Because aberrant activation of tyrosine kinases upstream of Shc signaling proteins has been implicated in resistance to tamoxifen--the most widely prescribed drug for treatment of estrogen receptor-positive breast cancer--we hypothesized that Shc isoforms may identify patients at increased risk of relapsing despite tamoxifen treatment.

Methods: Immunohistochemical analyses of PY-Shc and p66 Shc were performed on archival primary breast cancer tumors from a population-based cohort (60 patients, 9 relapses) and, for validation, an independent external cohort (31 patients, 13 relapses) in which all patients received tamoxifen as a sole systemic adjuvant prior to relapse.

Results: By univariate and multivariate analyses, the Shc proteins were very strong and independent predictors of treatment failure in both the population-based cohort (interquartile hazard ratio = 8.3, 95% confidence interval [CI] 1.8 to 38, P = 0.007) and the validating cohort (interquartile relative risk = 12.1, 95% CI 1.7 to 86, P = 0.013).

Conclusion: These results suggest that the levels of PY-Shc and p66 Shc proteins in primary tumors identify patients at high risk for relapsing despite treatment with tamoxifen and therefore with further validation may be useful in guiding clinicians to select alternative adjuvant treatment strategies.

Figure 1

Comparison of the PY-Shc-to-p66 Shc ratio in primary tumors as a function of disease recurrence. (a) Photomicrographs of PY-Shc and p66 Shc immunohistochemical staining patterns in primary tumors from patients who received tamoxifen and then either relapsed or did not relapse. Shc scores are shown in the insets. The left panel shows the staining patterns of two patients from the population-based cohort, and the right panel shows the staining patterns of two patients from the case-control cohort. Total magnification, ×200. (b) The ratio of PY-Shc to p66 Shc (Shc ratio), scaled 0 to 1, is shown (mean ± standard error) for primary tumors from patients who either relapsed or did not relapse. A comparison of the mean Shc ratios for patients in the population-based study with or without relapses is shown on the left side of the column graph (50 no relapses, 9 relapses; *P = 0.002). A comparison of the mean Shc ratios for patients in the case-control study with or without relapses is shown on the right side of the column graph (18 no relapses, 13 relapses; **P = 0.049). (c) Scatter histograms of the Shc ratio, on a log scale, observed in the patients' primary tumors as a function of relapse in the population-based and case-control cohorts. PY-Shc, tyrosine-phosphorylated Shc.

Figure 2

Relapse-free survival (RFS) according to Shc in patients with breast cancer. (a) Kaplan-Meier graphical analysis of RFS in patients from the population-based cohort partitioned by the median value for Shc (P = 0.013). (b) Kaplan-Meier graphical analysis of RFS in patients from the case-control cohort partitioned by the median value for Shc (P = 0.035).