Demographic features
A total of 52 male Asian patients harboring BRCA mutations were identified in the SYSUCC cohort. The median age at the time of diagnosis was 63.5 years (range, 4-86 years). Most patients (36/52, 69.2%) were aged 50-69 years. Fifteen patients (28.8%) had a family history of tumor, and only 3.8% (2/52) demonstrated multiple primary tumors. The prostate was the most common site of tumor disease in this cohort (19/52, 36.5%), followed by the colorectum (13/52, 25.0%), stomach (7/52, 13.5%), and lung (4/52, 7.7%). Only one male patient with breast cancer harboring a germline BRCA mutation was observed. The majority had stage III (15/52, 28.8%) or stage IV (28/52, 53.8%) disease. Sixteen patients (30.8%) tested positive for only BRCA1 mutations, of which 3 were germline and 13 were somatic. Thirty-three (63.5%) patients harbored only BRCA2 mutations, of which 4 were germline, 26 were somatic, and 3 displayed both germline and somatic BRCA2 mutations. We also found that three patients harbored both BRCA1 and BRCA2 somatic mutations. In addition, 13.5% (7/52) of the patients showed a microsatellite instability-high (MSI-H) phenotype, while 30.7% showed moderate to high TMB (≥10 mutations/Mb). The clinical characteristics of the SYSUCC cohort are summarized in Table 1.
The incidence of BRCA mutations in male patients was 6.0% (294/4871) in the TCGA cohort, and the majority of these patients were white. The median age at the time of diagnosis was 65 years (range, 34-88 years), and the patients were predominantly 50-79 years old. Carcinomas of the lung (57/294, 19.4%), bladder (46/294, 15.6%), stomach (35/294, 11.9%), head and neck (25/294, 8.5%), and colorectum (24/294, 8.2%), as well as cutaneous melanoma (48/294, 16.3%) were frequent tumors demonstrating BRCA mutations. However, prostatic cancer was only observed in 11 cases, and three patients had breast cancer. The majority of the patients had stage II (86/294, 29.3%) or stage III (28/52, 53.8%) disease. Similar to the findings in the SYSUCC cohort, 81 patients (27.6%) had a BRCA1 mutation, while 193 patients (65.6%) had a BRCA2 mutation. Patients with both BRCA1 and BRCA2 mutations (20/294, 6.8%) showed a median total mutation count of 2390 mutations (range, 264-15832 mutations), which was significantly higher than that in patients with either BRCA1 or BRCA2 mutations. The clinical characteristics of the TCGA cohort are summarized in Table 2.
Clinical characteristics of males and females with BRCAm
The clinical characteristics were compared between male and female patients with BRCAm, as shown in Table 2. The incidence of BRCAm (6.0 vs. 6.6%) as well as the age at diagnosis of tumor were similar between male and female patients, and no significant difference was observed (p=0.275 and p=0.15, respectively). However, the spectrum of tumors that occurred in males was obviously different from that in females. Carcinomas of the breast, ovary, uterus, and cervix frequently occurred in females with BRCAm, while a higher incidence of carcinomas in the lung, bladder, stomach, and head and neck, as well as cutaneous melanoma, was found in male BRCAm carriers (Figure 1A). Adenocarcinoma was the most common histological type in both groups, while there were more cases with melanoma, urothelial carcinoma, and squamous cell carcinoma in males (Figure 1B). In addition, stage III (24.5 vs. 11.5%) and stage IV (13.3% vs. 2.3%) disease were more common in males than in females. Interestingly, individuals with both BRCA1 and BRCA2 mutations were more frequently observed in females (14.1% vs. 6.8%).
Clinical characteristics of males with and without BRCAm
The mean age of male patients without BRCAm at the time of diagnosis was 61 years (range, 14-86 years), which was younger than that of male patients with BRCAm (p<0.001). No difference was observed in the ethnic distribution between groups. Notably, compared to non-BRCAm carriers, cutaneous melanoma (16.3 vs. 5.0%), lung cancer (19.4 vs. 11.8%), bladder cancer (15.6 vs. 5.6%), and stomach cancer (11.9 vs. 5.5%) accounted for a significantly higher proportion of the tumors diagnosed in the BRCAm group. There were fewer patients that had a diagnosis of renal cell carcinoma (4.8 vs. 12.3%) or prostatic carcinoma (3.7 vs. 10.6%) in the BRCAm group than in the non-BRCAm group (Table 2, Figure 1A). Histologically, adenocarcinoma was the most common type in both groups, but melanomas and urothelial carcinomas were more commonly found in the BRCAm group (Figure 1B). Patients with BRCAm were also likely to present a more advanced stage of disease (p=0.007) and higher total mutation counts than those without BRCAm (median, 322 vs. 63 mutations).
The mutational profiles of BRCA1/2 in males
The characteristics of BRCA1/2 mutations in male and female patients with a diagnosis of cancer are detailed in Table 3. A total of 438 BRCA1/2 variations were identified in the males in the TCGA cohort (details provided in Supplementary Table 1) and SYSUCC cohort (details provided in Supplementary Table 2). Mutations affecting BRCA1 and BRCA2 accounted for 29.0% (127/438) and 71.0% (311/438), respectively. For BRCA1, 21.8% (29/127) of the mutations were deleterious or likely deleterious. Similarly, 28.6% (89/311) of BRCA2 variations were identified as deleterious or likely deleterious. More than one BRCA1/2 mutation was observed in 17.3% (60/346) of the male patients. Missense mutations were the predominant mutational types of both BRCA1 and BRCA2, accounting for 70.1% (89/127) and 69.5% (216/311), respectively, followed by nonsense and frameshift mutations.
As shown in Figure 1C, BRCA2 mutation was more frequently detected than BRCA1 mutation regardless of the location of the tumor in males and accounted for 56.7-100.0% of the cases. Mutations simultaneously affecting both BRCA1 and BRCA2 mainly occurred in head/neck squamous cell carcinoma (18.8%) and cutaneous melanoma (12.5%). However, in terms of pathogenicity (Figure 1D), only a few BRCA1/2 mutations in cutaneous melanoma (8/48, 16.7%) and tumors located in the head and neck (5/27, 18.5%) and CNS (1/7, 12.5%) were deleterious. None of the BRCA1/2 mutations in the renal cell carcinoma cases included in this study were deleterious (0/14). More frequent deleterious mutations were identified in carcinomas of the colorectum (23/37, 62.2%), prostate (13/30, 43.3%), and stomach (18/42, 42.9%). Notably, all BRCA mutations in male breast cancer were deleterious (4/4). Compared to BRCA1/2 mutations in female patients, fewer deleterious (or likely deleterious) mutations affecting BRCA1 were detected in males (21.8 vs. 34.7%, p=0.032), while those affecting BRCA2 showed no difference between groups (28.6 vs. 25.8%, p=0.454). In addition, male patients displayed fewer frameshift mutations in BRCA1 than female patients (5.5 vs. 10.4%, p=0.013). In contrast, frameshift mutations in BRCA2 were likely more frequently found in males (15.1% vs. 9.5%), while no significant difference was observed.
Mutations on the linear BRCA1 or BRCA2 protein and its domains were mapped as shown in Figure 2. In accordance with the findings of previous studies, there was no obvious hotspot mutational region in either BRCA1 or BRCA2. In male BRCA1 mutation carriers, only 2 of 127 mutations (1.6%) were located in the RING domain that associates with BRCA1-associated RING domain protein 1 (BARD1) and catalyzes protein ubiquitylation. Eight mutations (6.3%) were found either at the BRCA1 C-terminus (BRCT) domain or at the serine-rich domain associated with BRCT, which facilitates phospho-protein binding, checkpoint activation and DNA repair. Similarly, in female BRCA1 mutation carriers, 3.1% (6/193) of mutations were located in the RING domain. In addition, 6.2% (12/193) and 4.7% (9/193) were mutated at the BRCT domain and serine-rich domain associated with BRCT, respectively. BRCA1 fusion mutations containing preferred partners, including NF1, FAM134C, BECN1, and LSM12, were more frequently detected in male carriers, while mutations affecting the E111 (E111*, E111Gfs*3) or R1443 (R1443*, R1443Q) sites were more commonly found in BRCA1 in female patients. In male BRCA2 mutation carriers, a total of 19 mutations (6.1%) were detected in the eight centrally located BRC repeats in BRCA2, which have been suggested to mediate the binding and regulation of RAD51 on resected DNA substrates. We also found 20.3% (63/311) of the mutations located in the BRCA2 DNA-binding domain, of which 5.1% (16/311) were in the helical domain, 14.2% (44/311) were in oligonucleotide binding folds, and 1.0% (3/311) were in the tower domain, which may affect BRCA2 binding to both single-stranded DNA and double-stranded DNA. In female BRCA2 mutation carriers, 6.3% (25/399) of the mutations affected BRC repeats, and 18.3% were located in the BRCA2 DNA-binding domain, of which 5.0% (20/399) were located in the helical domain, 11.3% (45/399) were located in oligonucleotide binding folds, and 2.6% (8/311) were located in the tower domain. In addition, frameshift mutations in BRCA2 at N1784 (N1784Kfs*3, N1784Tfs*3) were frequently observed in both male and female patients. Recurrent BRCA2 mutations at P606L/S, E832K/G, and T3033Lfs*29 were shown in males, while those at R1512C/H, K1691Nfs*15, S1882*, R2842C/H, E3342K, and K3416Nfs*11 appeared repeatedly in female BRCA2 mutation carriers.
Prognostic implications of BRCAm in males
Male BRCAm carriers with a diagnosis of malignancy were followed-up for 0.3-151.3 months, with a median of 25.9 months. In comparison, male patients without BRCAm were followed-up for 0.1-357.4 months, with a median of 22.9 months. Moreover, female patients with BRCAm were followed-up for 0.1-302.1 months, with a median of 26.2 months. Survival analyses were conducted in both the unmatched and matched cohorts. The survival curves of the three groups are shown in Figure 3. BRCAm in males was associated with a decrease in overall survival (OS) and progression-free survival (PFS) when compared to female patients with BRCAm in both the unmatched and matched cohorts (Figure 3A-D; p<0.001). No significant difference in OS was observed between male patients with and without BRCAm in either the unmatched (p=0.698; Figure 3A) or matched cohort (p=0.191; Figure 3E), but those with deleterious BRCAm displayed a significantly increased OS compared with non-BRCAm carriers in both the 1:3 (p=0.021; Figure 4A) and 1:6 matched models (p=0.042; Supplementary figure 1). Furthermore, among male patients with BRCAm, after matching for age and TNM stage, those with deleterious BRCAm also displayed an increased OS compared with patients with BRCAm of undetermined significance (p=0.027; Figure 4C). However, no difference in PFS was found in any comparisons between groups in males (Figure 3B, 3F, 4B, and 4D). Subgroup survival analysis was also conducted among male patients with either BRCA1, BRCA2 or both two mutations, but no difference in survival was found (Supplementary figure 2).
The associations between BRCAm and the survival outcomes of male patients in the subgroups of different tumor types are shown in Figure 5. BRCAm was associated with hazard ratios for OS of 0.61 (95% CI 0.39-0.94; p=0.05) and 0.60 (95% CI 0.39-0.94; p=0.05) in the subgroups of patients with bladder cancer and stomach cancer, respectively. In contrast, the hazard ratio for OS was 3.07 (95% CI 1.45-6.53; p<0.01) in glioma/glioblastoma patients with BRCAm. In addition, BRCAm was associated with hazard ratios for PFS of 2.42 (95% CI 1.22-4.81; p=0.01) and 3.24 (95% CI 1.15-9.08; p=0.02) in patients with prostatic cancer and in those with head and neck squamous cell carcinoma, respectively. The survival curves of OS and PFS between the groups of these tumors are shown in Figure 6.