Pre-Operative PARPi and Irradiation (POPI) in Women With an Incomplete Response to Neo-Adjuvant Chemotherapy for Breast Cancer

Neo adjuvant (Primary) chemotherapy has revolutionized the management of locally advanced breast. Two large prospective American studies have shown that NAC provides in vivo chemo-sensitivity information, and allows a greater percentage of women to have breast conserving therapy. Additionally and importantly, these two trials also showed that 20-30% of the women treated with NAC achieve a pathologic complete response (pCR) and have a better disease free and overall survival than those women who did not achieve pCR.

Unfortunately, 70-80% of patients receiving NAC do not achieve a pCR and many still must undergo a mastectomy due to an insufficient partial response. Researchers have attempted to increase the rate of pCR by adding radiation to NAC with mixed response rates. The varying rates of pCR in the above studies are likely due to the various chemotherapeutic agents used and timing of therapies yet also may represent the limitation of efficacy in combining these chemotherapy agents with radiation. What is needed is a better agent that can potentiate the effects of preoperative radiation.

One possible agent that may potentiate the effects of radiation is an inhibitor of Poly(ADP-ribose)-polymerase (PARP). PARP is a nuclear enzyme that recognizes deoxyribonucleic acid (DNA) damage and facilitates DNA repair. Cancer cells are often deficient in DNA repair. Deficiencies in DNA repair make these cancers more dependent on PARP. An inhibitor of PARP would further hamper the cancer cell's DNA repair capability. So theoretically, the efficacy of DNA damaging agents, such as radiation and chemotherapy, should be potentiated when these therapeutic modalities are combined with PARP inhibition.

Indeed, as expected, PARP inhibitors (PARPi), such as Veliparib, have been shown in pre-clinical studies to potentiate the effects of radiation and chemotherapy in several malignancies. Thus, we hypothesize that concurrent Veliparib and pre-operative breast irradiation, in women who have residual disease after NAC, will result in an increased tumor response rate. This improved tumor response will not only increase the rate of BCT, but possibly, by increasing the rate of pCRs, also improve overall survival.

However, before this hypothesis can be adequately tested, one must assess the safety of combining radiation and Veliparib. Consequently we propose a trial of Pre-Operative PARPi and Irradiation (POPI) in women with an incomplete response to NAC. It will be a standard 3+3 dose finding trial in which the MTD will be defined as the dose below the level at which >1 DLT is observed in 3-6 patients. Women with node positive disease prior to NAC and >1.0 cm residual breast disease and/or clinically positive nodal disease after NAC will be offered participation in this study. Four (4) dose levels of Veliparib will be evaluated with concurrent whole breast and regional nodal irradiation (WB/RNI). The starting dose of Veliparib will be 50 mg BID, will increase in 50 mg increments to a maximum of 200 mg BID and be delivered concurrently with 235 cGy QD x 16 to the breast and SCV/Axilla.