In addition to contraction, myoepithelia have diverse paracrine effects, including a tumor suppression effect. However, certain myoepithelial markers have been shown to contribute to tumor progression. Transforming growth factor-β (TGF-β) is involved in the transdifferentiation of fibroblasts to contractile myofibroblasts. We investigated whether TGF-β can upregulate potential myoepithelial markers, which may have functional and clinicopathological significance in breast cancer. We found that TGF-β induced SPOCK1 expression in MCF10A, MCF12A, and M10 breast cells and demonstrated SPOCK1 as a novel myoepithelial marker that was immunolocalized within or beneath myoepithelia lining ductolobular units. A functional study showed that overexpression of SPOCK1 enhanced invasiveness in mammary immortalized and cancer cells. To further determine the biological significance of SPOCK1 in breast cancer, we investigated the expression of SPOCK1 in 478 invasive ductal carcinoma (IDC) cases through immunohistochemistry and correlated the expression with clinicopathological characteristics. SPOCK1 expression was significantly correlated with high pathological tumor size (P = 0.012), high histological grade (P = 0.013), the triple-negative phenotype (P = 0.022), and the basal-like phenotype (P = 0.026) and was correlated with a significantly poorer overall survival on univariate analysis (P = 0.001, log-rank test). Multivariate Cox regression analysis demonstrated that SPOCK1 expression maintained an independent poor prognostic factor of overall survival. Analysis of SPOCK1 expression on various non-IDC carcinoma subtypes showed an enrichment of SPOCK1 expression in metaplastic carcinoma, which is pathogenetically closely related to epithelial-mesenchymal transition (EMT). In conclusion, we identified SPOCK1 as a novel TGF-β–induced myoepithelial marker and further demonstrated that SPOCK1 enhanced invasion in breast cancer cells and correlated with poor prognosis in breast cancer clinical samples. The enrichment of SPOCK1 expression in metaplastic carcinoma and the correlation between SPOCK1 expression and high histological grading and basal-like phenotypes in IDC evidence an association between SPOCK1 and EMT.

Both stromal tumor-infiltrating lymphocytes (sTILs) and programmed death-ligand 1 (PD-L1) affect responses to immunotherapy; however, the extent of sTIL and PD-L1 expression within various metaplastic components in metaplastic breast carcinoma (MBC), which are critical for the characterization of immune microenvironments, remains unreported. We profiled sTIL infiltration and PD-L1 expression in different metaplastic components of specimens from 82 MBC patients. The overall positivity for high or intermediate (H/I) sTIL, immune cell-PD-L1 (IcPD-L1), and tumor cell-PD-L1 (TcPD-L1) was 34.1%, 47.6%, and 17.1%, respectively, but differences specific to MBC subtypes and each metaplastic component existed. Squamous cell carcinoma exhibited the highest positivity rates of sTIL(H/I) (50.0%) and IcPD-L1 (66.7%), while matrix-producing carcinoma had the lowest respective rates (14.3% and 28.6%). The positivity rates of sTIL(H/I) and IcPD-L1 were the highest in squamous component (Sq) and the lowest in chondroid component (Ch). All cases that had discordant sTIL categories between carcinoma of no special type (NST) and metaplastic components showed sTIL(H/I) positivity higher in Sq, but lower in spindled component (Sp) and Ch. While there was no pattern of higher IcPD-L1-positivity in Sp, six of the seven cases that were TcPD-L1-discordant between NST and Sp were TcPD-L1-positive in Sp, suggesting a trend for higher TcPD-L1 in Sp. The diagnostic predictability of total tumor IcPD-L1 positivity based on IcPD-L1 positivity in Sq and Ch was 95.2% and 33.3%, respectively. Multivariate analysis showed that sTIL(H/I) positivity, but not PD-L1 positivity, correlated with better survival. Our data implicate distinct immune microenvironments in different metaplastic components in MBC, which may have immunopathologic, diagnostic, and therapeutic significance.

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