Elizabeth Santana Dos Santos

The germline landscape of hereditary breast cancer has been characterized predominantly in populations of European ancestry, with limited evidence from populations with different demographic histories. We investigated germline diversity and genotype–phenotype associations in a single-center ambispective cohort at a tertiary referral cancer center in Brazil. Among 10,098 individuals who underwent germline genetic testing, 503 adults with invasive or microinvasive breast cancer met the predefined eligibility criteria and carried 514 pathogenic or likely pathogenic germline variants. Analyses assessed gene distribution, recurrent and founder variants, ecological diversity metrics, and associations with clinicopathological characteristics and survival outcomes. BRCA1 (31.6%) and BRCA2 (21.7%) were the most frequently altered susceptibility genes, followed by TP53 (13.1%), including the Brazilian founder variant TP53 p.R337H (10.7%). Diversity analyses indicated substantial heterogeneity beyond BRCA1/2. In exploratory unadjusted analyses, BRCA1-associated tumors more frequently exhibited triple-negative phenotype, high histological and nuclear grade, elevated Ki-67, and increased tumor-infiltrating lymphocytes, whereas tumors associated with BRCA2, ATM, CHEK2, and mismatch repair genes more frequently exhibited luminal phenotypes. Recurrent variants included alleles previously reported in different geographic and population contexts. Exploratory survival analyses detected no statistically significant differences among genetic groups within a five-year analytical horizon. These findings describe a heterogeneous germline spectrum and exploratory genotype–phenotype associations in a Brazilian cohort. Heterogeneous genetic testing coverage and the absence of individual genomic ancestry assessment limit interpretation; the findings should not be considered ancestry-specific or nationally representative. Further studies with uniform genetic testing and genomic ancestry assessment are warranted in broader Brazilian and Latin American cohorts.

Poly(ADP-ribose) polymerase inhibitors (PARPis) have demonstrated remarkable efficacy in tumors carrying BRCA1/2 pathogenic variants (PVs) through the mechanism of synthetic lethality. PVs in other homologous recombination (HR) genes may also impair homologous recombination repair and confer sensitivity to PARPis; however, their predictive value remains uncertain and appears to vary according to the affected gene and tumor type. We review and critically discuss the current evidence regarding the predictive value of non-BRCA HR gene pathogenic variants as biomarkers of PARPi sensitivity across ovarian, breast, prostate, and pancreatic cancers. A narrative review was conducted between October 2023 and December 2025, first identifying pivotal clinical trials of PARP inhibitors across ovarian, breast, prostate, and pancreatic cancers, followed by a targeted search of PubMed, Embase, Web of Science, and Google Scholar for relevant preclinical and clinical studies. Seventeen clinical studies and multiple preclinical reports were analyzed regarding genomic frequency, HRD association, and treatment response. Preclinical studies consistently demonstrated increased PARPi sensitivity in models with alterations in several non-BRCA HR genes. Clinical evidence, however, was heterogeneous. PALB2 demonstrated the strongest and most consistent association with PARPi benefit across tumor types, while RAD51C and RAD51D also showed clinically meaningful activity, particularly in ovarian cancer. In contrast, evidence supporting PARPi sensitivity in tumors harboring ATM, CHEK2, CDK12, and several other HR gene alterations remained limited or inconsistent. Differences in gene function, biallelic inactivation, variant type, and current limitations of HRD companion diagnostic assays likely contribute to the observed variability in clinical response. Non-BRCA HR gene alterations represent promising predictive biomarkers for PARPi therapy but should not be considered a homogeneous group. Future biomarker-driven studies integrating comprehensive genomic profiling and functional assessment of homologous recombination deficiency are needed to refine patient selection and optimize the clinical application of PARPis beyond BRCA1/2-associated cancers.

Characteristics of 12 case-control datasets from the ENIGMA consortium partners.

Detail description of the functional categorization of analyzed CHEK2 missense variants.

Frequencies of all reported germline CHEK2 variant carriers and carriers of variants concordantly categorized by functional our kinase assays in breast cancer patients and controls in 12 analyzed population datasets.

List of all analyzed CHEK2 variants with results of KAP1/CHK2 kinase and localization assays and the results from recent previously published functional analyses of the CHEK2 VUS.

Results of KAP1 and CHK2 kinase assays for 430 successfully analyzed missense CHEK2 variants (shown as an average relative CHK2 kinase activity). Bars are colored as functionally WT-like (green), intermediate (IM; yellow), and impaired (ID; red), respectively, with thresholds for IM variants (0.428 and 0.479) and ID variants (0.705 and 0.710) for KAP1 and CHK2 assays, respectively (dashed lines). Error bars represent standard errors of mean. Color/gray letters for protein variants indicate concordant/discordant functional assays result, respectively. Blue boxes denote conserved CHK2 domains. DNL, variants that do not localize into the nucleus.

Kinase KAP1 and CHK2 assays (A). The bar graphs show results of kinase assays for 430 CHEK2 missense variants. In both assays, variants with normalized relative CHK2 activity (mean WT-activity = 1) exceeding that of the weakest signal of WT replicas (not shown) were categorized functionally WT-like, variants with normalized signal intensity lower than the strongest signal for any of kinase-dead/empty EGFP vector controls (in-frame exon 7 deletion–p.D265_H282del; not shown) were categorized as functionally impaired. Variants with normalized CHK2 activities between these ranges were categorized functionally intermediate (0.428–0.705 and 0.479–0.710 for KAP1 and CHK2 assay, respectively; indicated by red and yellow dashed lines). Scatterplot combines results from both assays showing 340 concordant (circles) and 90 discordant (crosses) variants. The nuclear-to-cytoplasmic ratio (B) bar graph (left) displays all missense variants and a set of protein-truncating CHEK2 variants (dark red bars at left, zoomed part of the graph). The missense variants, p.R521W and p.R521Q, with an aberrant localization are highlighted as bright-red bars; the arrows denote WT (green bar) and catalytically-dead in-frame p.D265_H282del variant (white bar). The highest and lowest mean nuclear/cytoplasmic ratio values from all WT replicates are indicated by green dashed lines. Of all missense variants analyzed by ScanR microscopy, only codon 521 alterations revealed aberrant intracellular localization with intense cytoplasmic positivity (right), reminiscent of mislocalization of the c.1100delC (p.T367fsX; size bar, 10 μm) variant. In comparison, the in-frame deletion p.D265_H282del revealed normal intranuclear accumulation, similar to WT. C, Scatter plots depicting correlations between assays performed in this study and previous analyses of CHEK2 VUS. Studies of Kleiblova et al. (17) and Boonen et al. (18) used phosphorylation of KAP1 as a functional readout whereas the study of Delimitsou et al. (25) used a yeast growth retardation assay. The dots are colored according to the results of the KAP1 assay in this study (red, impaired; yellow, intermediate; green, wild-type–like). Blue line represents linear regression, R, correlation coefficient; P, P value. The scatter plot does not show the p.Arg512Trp variant classified by Boonen et al. as intermediate with impaired nuclear localization in our localization assay.

Detail description of the functional categorization of analyzed CHEK2 missense variants.

Presence of analyzed CHEK2 missense variants categorized according to the functional assays in patients with breast cancer (BC pts; red numbers) and matched controls (dark green numbers). The association with breast cancer risk (odds ratio; OR) were calculated for prevalent variants having ≥10 carriers among patients or controls, respectively. Colors of the numbers in the last column highlight significant association with moderate-or-higher risk (red; OR > 2), low risk (OR < 2), protective variants (green) or variants without significant impact on breast cancer risk (black). Gray rows display variants that were discordant in the kinase assays. DNL, variants that do not localize into the nucleus.