- Luminal B (HER2 negative) subtype is the most diversiform type of breast cancers, with a high Ki-67 proliferation index (>20%) or/and low progesterone (PR; <20%) with various intensity and distribution of hormone receptors. Considerable difference has also been noticed in disease outcome, wherefore there is the need for a more detailed classification of this tumor subtype. The clinical and pathologic parameters of 147 luminal B (HER2 negative) breast cancers were examined. The expression of hormone receptors in correlation with other prognostic factors and disease outcome was analyzed by Kaplan-Meier curves and multivariate Cox regression analysis. The Kaplan-Mayer analysis showed that low positivity of estrogen (ER) and PR receptors in tumors was associated with a significantly worse disease outcome (overall survival (ER), p=0.020; disease free survival (ER), p=0.019; overall survival (PR), p=0.026; disease free survival (PR), p=0.038)), unlike Ki-67, which did not show a statistically significant connection (overall survival, p=0.343; disease free survival, p=0.322). The intensity of receptor staining and Ki-67 relative to other histopathologic prognostic factors showed a statistically significant correlation solely with histologic grade of tumor. By using the Cox regression model, PR proved to be an independent prognostic factor for overall survival (p=0.004) and disease free survival (p=0.029). The luminal B (HER2 negative) breast cancer with low expression of hormone receptors, independent of the Ki-67 proliferation index, and in correlation with a higher histologic grade, could be a unique subtype of cancer.
Keywords: Breast neoplasms; Croatia; Disease-free survival; Receptors, estrogen; Receptors, progesterone.