Radiation Therapy With or Without Olaparib in Treating Patients With Inflammatory Breast Cancer

Inclusion Criteria: * Patients must have inflammatory breast cancer without distant metastases. All biomarker subtype groups (estrogen receptor \[ER\], progesterone receptor \[PR\], HER2) are eligible. Inflammatory disease will be defined per American Joint Committee on Cancer (AJCC) 8th edition with documentation by history/exam and pathology at the time of diagnosis. * All patients must have completed neoadjuvant chemotherapy prior to mastectomy. The chemotherapy regimen is at the discretion of the treating physician but it is recommended that it include at least 4 cycles of anthracycline and/or taxane-based therapy (plus targeted therapy for patients with HER2+ disease). Response to chemotherapy is not a criterion for eligibility (both complete responders and those with residual disease are eligible). Please note that although pathologic complete response (pCR) is not required or excluded, pCR status must be determined post-surgery prior to randomization. * All patients must have undergone modified radical mastectomy (with negative margins on ink) with pathologic nodal evaluation (from level I and II axillary lymph node dissection \[ALND\]) at least 3 weeks and no more than 12 weeks prior to randomization, unless they receive additional chemotherapy after mastectomy. Patients must not have gross residual tumor or positive microscopic margins after mastectomy. * Additional adjuvant chemotherapy after surgery is allowed at the discretion of the treating physician, either co…