In the Keynote 522 trial for early-stage TNBC, adding pembrolizumab to chemotherapy resulted in only a modest improvement in pathological complete response (pCR). Surprisingly, this small initial gain translated into much more robust and significant long-term improvements in event-free and overall survival.

For high-risk early-stage breast cancer patients with a germline PALB2 mutation, clinicians would consider using an adjuvant PARP inhibitor off-label. This is justified by PALB2's biological similarity to BRCA2 and promising response data from the metastatic setting, providing an option for patients who meet Olympia trial criteria but have a different mutation.

For de novo metastatic, PD-L1 positive TNBC patients with a BRCA mutation, experts prefer an ADC with immunotherapy over a PARP inhibitor. This choice is driven by the potential for longer-lasting responses with the ADC/IO combination, even though PARP inhibitors directly target the underlying genetic mutation.

The combination of olaparib and radium-223 improves progression-free survival in an unselected patient population. The mechanism isn't reliant on pre-existing BRCA mutations. Instead, radium (an alpha-emitter) induces DNA breaks, and olaparib prevents the PARP enzyme from repairing this new damage, thus sensitizing the tumor to the radiopharmaceutical.

For high-risk, HR+ patients with germline BRCA mutations, data suggest they derive less benefit from CDK4/6 inhibitors. A practical approach is to give one year of the PARP inhibitor olaparib first, followed by a CDK4/6 inhibitor, capitalizing on the delayed initiation allowance in major trials.

A nuanced approach to PARP inhibitors involves reserving combinations for BRCA2 patients with clear, aggressive clinical features like high-volume disease or liver metastases. This strategy balances potent efficacy against toxicity for a molecularly defined but clinically heterogeneous group, avoiding overtreatment of those with more indolent disease.

Recent trial data shows that patients with somatic BRCA1/2 mutations (found only in the tumor, not inherited) can achieve significant responses to PARP inhibitors. This finding supports routine tumor genomic testing to identify more candidates for this targeted therapy beyond just those with germline mutations.

Clinical trial data suggests immunotherapy's timing is crucial in early-stage TNBC. Given with chemotherapy before surgery (neoadjuvant), it improves outcomes. However, when given alone after surgery (adjuvant), the IMPASSION 030 trial showed no benefit and was halted for futility, indicating pre-surgical tumor priming is essential.

In high-risk, BRCA-positive patients eligible for both, clinicians favor giving a PARP inhibitor first. The rationale is based on established survival data, shorter one-year duration, and emerging biological evidence suggesting BRCA2-mutated tumors may be resistant to CDK4/6 inhibitors due to concurrent RB gene loss.