Oncologist. 2021 May 22.
Homologous recombination (HR) is a highly accurate DNA repair mechanism. Several HR genes are established cancer susceptibility genes with clinically actionable pathogenic variants (PVs). Classically, BRCA1 and BRCA2 germline PVs are associated with significant breast and ovarian cancer risks. Patients with BRCA1/BRCA2 PVs display worse clinical outcomes but respond better to platinum-based chemotherapies and PARP inhibitors, a trait termed as "BRCAness". With the advent of whole-exome sequencing and multigene panels, PVs in other HR genes are increasingly identified among familial cancers. As such, several genes such as PALB2 are reclassified as cancer predisposition genes. But, evidence for cancer risks remains unclear for many others. In this review, we will discuss the cancer predispositions and treatment implications beyond BRCA1/BRCA2, with a focus on 24 HR genes: 53BP1, ATM, ATR, ATRIP, BARD1, BLM, BRIP1, DMC1, MRE11A, NBN, PALB2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, RIF1, RMI1, RMI2, RPA1, TOP3A, TOPBP1, XRCC2, XRCC3. IMPLICATIONS FOR PRACTICE: Our review provides a quick and comprehensive read to both experts and amateurs to the topic. Interested readers are also directed to comprehensive reviews of specific topics discussed in the review (e.g. clinical trials on PARP inhibitors and other targeted inhibitors of HR proteins). Our table summarizes the risk estimates based on some of the largest and most recent studies, facilitating the reclassification of these HR genes as cancer predisposition genes. We have also highlighted several potential research questions in our review.