Association of low tumor RNA integrity with response to chemotherapy in breast cancer patients

The CAN-NCIC-MA22 phase I/II clinical trial evaluated women with locally advanced or inflammatory breast cancer treated with epirubicin and docetaxel at 2 or 3 weekly intervals in sequential cohorts. The relationship between various biomarkers and treatment response was assessed. Breast biopsy cores were obtained from 50 patients pre-, mid-, and post-treatment. Immunohistochemical staining was performed to determine baseline levels of estrogen receptor (ER), progesterone receptor (PR), Her2/Neu protein (HER2), and topoisomerase II (Topo 2), expressed as percent positive stain. Tumor RNA integrity (RIN) and tumor cellularity were measured pre-, mid- and post-treatment by capillary electrophoresis and light microscopy after hematoxylin/eosin staining, respectively. Associations between 1) maximum RIN and 2) tumor cellularity at the three time points with baseline levels of ER, PR, Her2, and topo II were assessed using Spearman and Pearson correlation coefficients. Associations between RIN and tumor cellularity with chemotherapy dose level or pathologic response were assessed using one-way ANOVA. In this study, we observed that low mid-treatment maximum RIN (but not tumor cellularity) was associated with high chemotherapy drug dose level (P = 0.05) and eventual pathologic complete response (pCR) (P = 0.01). Post-treatment, low maximum RIN was found to be associated with low tumor cellularity (P = 0.004), and low tumor cellularity with pCR (P = 0.01). Post-treatment tumor cellularity was lowest in patients with tumors having high baseline PR levels (P = 0.05). The association of mid-treatment RIN with drug dose level and with pCR suggests that tumor RIN may represent an important new biomarker for measuring response to chemotherapy in breast cancer patients.