Biologic Correlative Taxotere/AC

Breast cancer and systemic chemotherapy: Systemic chemotherapy for operable breast cancer significantly decreases the risk of relapse and death. However, it is not possible to identify those patients at the outset who are likely to respond to adjuvant treatment and which type of treatment should be used. Adjuvant treatment given before surgery (neoadjuvant therapy) has a number of advantages in breast cancer, including a reduction in the requirement for mastectomy. Access to the primary tumor during early treatment allows for in vivo testing for predictive markers obtained by core biopsies that occur with successful treatment.

Predictive markers in breast cancer: Prognostic factors like tumor size and nodal involvement are important indicators for breast cancer survival but have not been shown to be predictive of sensitivity to chemotherapy. With endocrine therapy, the prime example of a predictive marker is estrogen receptor (ER) expression, which predicts for response to tamoxifen and other endocrine treatments. However, predictive markers for chemotherapy are not established. Overexpression of c-erbB-2 might be associated with decreased response to CMF and increased response to anthracycline-based treatment, but these observations are still contentious. Expression of topoisomerase II may also reflect responsiveness to anthracycline chemotherapy. Recently, some emerging data also suggest that c-erbB2 may be a marker of taxane sensitivity. As such, we lack predictive biomarkers that could give early information on how effective chemotherapy is and whether additional treatment might be beneficial. A test for chemotherapy sensitivity, equivalent to ER in predicting response to endocrine therapy, would greatly facilitate treatment decisions so that in an ideal scenario, the treatment of each individual patient could be based on specific features of her disease.

Neoadjuvant chemotherapy: Preoperative chemotherapy for large tumors (>3cm) or inoperable breast cancer is well established and is the standard of care for locally advanced breast cancer. Data from large series of patients have demonstrated that preoperative (neoadjuvant) chemotherapy leads to significant reduction of tumor size (downstaging) and improves both the rate and the cosmetic results of breast-conserving surgery. A recent large randomized trial involving 1,523 patients compared preoperative and postoperative chemotherapy (NSABP B-18). Although results of this study have shown no difference in disease-free survival and survival in women on preoperative or postoperative doxorubicin and cyclophosphamide chemotherapy, significant downstaging of tumors was achieved so that more patients who received preoperative therapy were able to undergo breast-conserving surgery. The rate of breast conservation in NSABP B-18 was 85% in patients with tumors greater than 3 cm, with less than 5% of patients reported to have progressive disease while receiving neoadjuvant chemotherapy.

cDNA arrays: High-Throughput Quantitative Profiling of Gene Expression: With the advent of high-throughput quantitation of gene expression and cDNA technology, it is now possible to study expression of many genes simultaneously to characterize expression patterns in different breast cancers that may distinguish molecular phenotypes associated with clinical response to a treatment. In a recent report, a molecular classification of leukemia was demonstrated. Bone marrow aspirates taken from 38 patients with acute leukemia were evaluated for expression of 6,817 human genes. The 50 best discriminating genes were used to create a predictive index that was then applied to new samples and was found to accurately assign them as AML or ALL.

Preliminary data for differential patterns of gene expression in responders vs non-responders of Taxotere chemotherapy: We conducted a pilot study to investigate gene expression patterns on core biopsies of human breast cancers in responders and non-responders to Taxotere chemotherapy.

RNA was isolated from core biopsies of primary breast cancers taken from women before initiation of Taxotere chemotherapy. Clinical response was assessed after 12 weeks of treatment. We compared patterns of gene expression statistically in order to identify genes differentially expressed between responders and non-responders to this single chemotherapeutic agent.

Overall, these genes efficiently cluster tumors into 3 groups: CR, PR, and NR. We have selected 2337 genes from these data for further analysis. As expected, the majority of these genes show heterogeneous expression patterns independent of treatment response, but six large gene clusters (approximately 180 genes) appear to predict likelihood of response to Taxotere therapy. Consistent with an apoptosis-induction mode of action for taxanes, responsive tumors appear to have higher expression of stress-related proteins, such as mitochondrial proteins involved in apoptosis (cytochromes, proteasome subunits), and higher levels of motility-related microfilament proteins (actin, myosin, and tropomyosin). Non-responders patterns are more complex but show elevated levels of some microtubule proteins presumed to be targets of Taxotere therapy (tubulins, tubulin-interacting proteins) and elevated levels of inflammatory-response genes. Surprisingly, non-responders also showed elevated proliferation (KI67) and oncogene (ABL1, MYC and JUNB) expression levels. This molecular portrait of Taxotere resistance differs from the expected profiles of general chemoresistance. Quantitative RT-PCR and immunohistochemistry studies to confirm these differential gene patterns of expression are in progress for all 40 patients.