Cell synthesis of heat shock (stress-response) proteins is increased by a variety of environmental and pathophysiological stressful conditions. The 70-kd heat shock protein (hsp70) is thought to be involved in protein-protein interactions including those of the protein products of the human c-myc on-cogene and the p53 (also known as TP53) tumor suppressor gene.
The purpose of this study was to investigate whether elevated hsp70 expression may be an indicator of biological stress experienced by a breast cancer and may, therefore, predict disease outcome.
Levels of hsp70 were determined by Western blot analysis in primary breast tumors from patients with negative axillary lymph nodes. We performed exploratory data analyses on a set of 162 primary breast cancers and constructed prognostic indexesof hsp70 expression levels. The optimal cutpoint for hsp70 expression was considered to be the value yielding the greatest separation for disease-free survival for the resulting two groups of patients. That cutpoint was then validated in a set of 345 tumors by univariate and multivariate analyses. Data were analyzed for overall survival, disease-free survival, tumor size, and patient age, as well as estrogen receptor and progesterone receptor status, ploidy (DNA content), and percentage of cells in S phase as determined by flow cytometry.
Expression of hsp70 emerged as a useful prognostic factor, both in univariate and in multivariate analyses. Patients whose tumors had high expression of hsp70 had significantly shorter disease-free survival ( P = .006). The other statistically significant factors were S-phase fraction ( P = .008) and tumor size ( P = .01). For patients who received adjuvant therapy, hsp70 was the only independent predictor of disease recurrence ( P = .05). For those with tumors 1-3 cm in diameter, hsp70 ( P = .008) and S-phase fraction ( P = .02) were statistically significant predictors of recurrence.
Measurement of hsp70 expression in primary tumors from patients with node-negative breast cancer may be useful in identifying patients at high risk for disease recurrence and thus may affect decisions regarding treatment after surgery.
Future studies should be performed to determine if detection of hsp70 by immunohistochemistry can be used to predict clinical outcome and to betterunderstand the relationships between hsp70 and the effects of various treatment modalities.