Breast cancer is the most frequently diagnosed cancer with an incidence rate of 11.7% of newly diagnosed female cancers and the first most common cause of cancer mortality in women worldwide [13]. Triple-negative breast cancer (TNBC) accounts for 20% of all molecular subtypes of breast cancer [14]. Although significant benefits of new targeted therapy and immunotherapy have been reported in the past few decades. Due to the high heterogeneity and few genetic targets, these tumors have the worst prognosis among all of the breast cancer subtypes and the overall survival rate within five years is less than 70% [15]. Traditional clinicopathological parameters, tumor-node-metastasis (TNM) staging system and single molecular markers have obvious limitations in predicting prognosis. It is necessary to identify the effective prognostic biomarkers of TNBC and establish the relevant prognostic risk prediction model. Multiple studies have reported that mutations in HRD-related genes are associated with the prognosis of multiple tumors, as well as the efficacy of PARP inhibitors. However, there is no research involving any transcriptomics about HRD. In this study, we construct a prognostic risk model based on transcriptome data of HRD. This signature could be used to efficiently determine the overall survival time of TNBC patients.
In this study, we screened out 110 TNBC samples with HRD scores according to the TCGA breast cancer dataset and HRD database. the DEGs were identified from HRD tumor samples and non-HRD tumor samples in TNBC patients. After WGCNA analyses, univariate, LASSO and multivariate Cox regression analyses, MUCL1, IVL, FAM46C, CHI3L1, PRR15L and CLEC3A were screened out as prognostic genes ultimately to develop the prognostic model. These genes contained in the signature have previously been reported to be associated with different cancer in various ways.
Mucin-like 1 (MUCL1) is a gene encoding a low molecular weight glycoprotein with high similarity to sialomucins, which was only expressed in salivary glands and breast tissues. It was identified as a breast-specific gene for breast cancer micrometastasi [16]. Most recently, Liu Liang et al. used IHC technology to detect the expression level of MUCL1 in paraffin-embedded tissues of 89 triple negative breast cancer patients and found that high MUCL1 expression is significantly correlated with high recurrence and death rates in triple negative breast cancer patients [17]. In additional, several studies have shown that MUCL1 expression strongly correlates with clinical stage of TNM and the status of axillary lymph node metastasis[17]. Involucrin (IVL), a component of keratinocyte crosslinked envelope, is found in the cytoplasm and crosslinked with membrane proteins by transglutaminase. This gene is mapped to 1q21, among calpactin I light chain, trichohyalin, profillaggrin, loricrin, and calcyclin. Recently, IHL has been identified as a novel hub gene that shows a significant up-regulation in colon adenocarcinoma as compared to normal tissue [18]. So far, there is little research on IVL in TNBC. only one study reported that 6-mRNA signature including IVL may act as a potential prognostic biomarker in patients with TNBC[19]. Family with sequence similarity 46, member C (FAM46C) is a member of the FAM46 family, it is located on chromosome 1p12 and seems to play a role in the regulation of translation by acting as an mRNA stabilizing factor. its abnormal deletions in tumor tissues were confirmed in multiple myeloma[20] and gastric cancer[21]. Zhang, et al reported that FAM46C was downregulated in hepatocellular carcinoma (HCC)and induced cell apoptosis through regulating Ras/MEK/ERK pathway [22]. In additional, FAM46C was downregulated in prostate cancer to inhibit cell proliferation and cell cycle progression and promote apoptosis through PTEN/AKT signaling pathway[23]. However, there is no research on FAM46C in TNBC. CHI3L1, on human chromosome 1q32.1, encodes a secreted glycoprotein called YKL-40, which plays an important role in inflammation, angiogenesis, radioresistance, and cancer progression. Overexpression of CHI3L1 have been de described in various types of cancer, including oligodendroglia, glioblastoma, osteosarcoma, breast, and small-cell lung cancers[24, 25]. YKL-40 expression was significantly upregulated in NSCLC tissues, and associated with poor prognosis and shorter survival [25]. PRR15L, also known as ATAD4, which encodes a protein of unknown function, to date, no report has been ascribed to this function of this gene. C-type lectin domain family 3 member A (CLEC3A), belonging to the superfamily of C-type lectins, is known to associate with cell adhesion which influenced results in tumor cell proliferation and metastasis[26, 27]. It was reported that CLEC3A expressed initially in cartilage and was associated with osteoarthritis. Recently, Ni, J et al [28] figured out that high CLEC3A expression significantly correlated with poor prognosis in IDC patients and promoted invasion and metastasis of breast cancer through activating PI3K/AKT signaling. Our findings suggest that these genes may be acted as important biomarkers to predict survival outcomes in patients with TNBC. If we can explore their specific mechanisms of action in triple-negative breast cancer more extensively and in-depth, it is likely that they can be used as new cancer biomarkers.
After identifying the six prognostic genes, the risk score model of HRD signature was developed and investigated for its prognostic value in TNBC patients, a clear separation was observed in the survival curve between patients in high-risk and low-risk subgroups, which was evaluated as a category variable (divided by median cutoff). We also found that the low-risk group had a very low proportion of deaths. Furthermore, we performed a stratification analysis, and the results suggested that 6-gene risk score in clinical subgroups (N0 stage, N1 + N2 + N3 stage, stage I + stage II, T1 + T2 stage) could still better predict the prognosis of TNBC. Then the univariate and multivariate Cox regression analysis showed that 6-gene risk score could be an independent factor to evaluate the prognosis. Finally, we developed a nomogram to guide clinical practice including AJCC-stage, HRD score, T stage, and N stage, and risk score to construct a nomogram to predict the 3-year and 5-year survival of TNBC patients. when compared with the TNM stage, 6-gene risk score showed the even better predictive ability in the ROC analysis.
However, we acknowledge several limitations in our study. Firstly, our study only focused on the large-scale mRNA sequencing data from the TCGA platform. the results report may be biased. Secondly, we searched the Gene Expression Omnibus (https://www.ncbi.nlm.nih.gov/geo/) for external validation, but many data sets have no prognostic OS information. Thirdly, in this study, the gene function and participation mechanism of six-gene models have not been clarified, and the relationship with the occurrence and development of breast cancer needs to be further confirmed by research under in vitro and in vivo conditions.