Expression of cancer-associated fibroblast-related proteins differs between invasive lobular carcinoma and invasive ductal carcinoma

Cancer-associated fibroblasts (CAFs) are classified into various functional subtypes such as fibroblast activation protein-alpha (FAP-alpha), fibroblast specific protein-1 (FSP-1), platelet-derived growth factor receptor-alpha (PDGFR-alpha), and PDGFR-beta. In this study, we compared the expression of CAF-related proteins in invasive lobular carcinoma (ILC) with those in invasive carcinoma of no special type (NST) and assessed the implications of the differences observed. Using tissue microarrays of 104 ILC and 524 invasive carcinoma (NST) cases, immunohistochemistry for CAF-related proteins [podoplanin, prolyl 4-hydroxylase, FAP-alpha, FSP-1/S100A4, PDGFR-alpha, PDGFR-beta, and chondroitin sulfate proteoglycan (NG2)] was conducted. In invasive carcinoma (NST), tumor cells expressed a high level of PDGFR-alpha, whereas ILC tumor cells expressed high levels of podoplanin, prolyl 4-hydroxylase, FAP-alpha, and FSP-1/S100A4. In stromal cells of invasive carcinoma (NST), high expression levels of prolyl 4-hydroxylase, PDGFR-alpha, and NG2 were observed, whereas ILC stromal cells expressed high levels of FAP-alpha, FSP-1/S100A4, and PDGFR-beta. In ILC, tumoral FSP-1/S100A4 positivity was associated with higher Ki-67 labeling index (p = 0.010) and non-luminal A type cancer (p = 0.014). Stromal PDGFR-alpha positivity was associated with lymph node metastasis (p = 0.011). On survival analysis of entire cases, tumoral FSP-1/S100A4 positivity (p = 0.002), stromal podoplanin positivity (p = 0.041), and stromal FSP-1/S100A4 negativity (p = 0.041) were associated with shorter disease-free survival; only tumoral FSP-1/S100A4 positivity (p = 0.044) was associated with shorter overall survival. In ILC, the expression of FAP-alpha and FSP-1/S100A4 was higher in both tumor and stromal cells than that observed in invasive carcinoma (NST). These results indicate that CAFs are a potential target in ILC treatment.