GSTPi-positive tumour microenvironment-associated fibroblasts are significantly associated with GSTPi-negative cancer cells in paired cases of primary invasive breast cancer and axillary lymph node metastases

Breast cancer is the second leading cause of death from cancer of women in the United States. Most patients with oestrogen receptor-negative breast cancer cells are treated with chemotherapeutic agents (Gonzales-Angulo et al, 2007). A subpopulation of such patients subsequently develop resistance to treatment, leading to the life-threatening progressive disease (Gonzales-Angulo et al, 2007). Role of various molecular mediators in the development of drug resistance by cancer cells have been reported. One such mediator is glutathione S-transferase Pi (GSTPi), a member of GST supergene family (Su et al, 2003; Arai et al, 2008). GSTPi catalyses reactions that result in covalent conjugation of reduced glutathione with electrophile compounds such as carcinogens and cytotoxic drugs (Brockstedt et al, 2002; Van Emburgh et al, 2008). The resulting product is hydrophilic and less toxic, and is readily excreted, thereby protecting the GSTPi protein-positive normal cells from the adverse effects of carcinogens (Sawaki et al, 1990). Reduction or loss of GSTPi protein expression has been reported to occur mainly by epigenetic mechanism in several forms of cancer, including breast, leading to suggestions that such loss may result in additional genetic damage in cancer cells and accelerated progression of disease (Randall et al, 1990; Toffoli et al, 1992; Green et al, 1993; Moskaluk et al, 1997; Esteller et al, 1998; Jhaveri and Morrow, 1998; Montironi et al, 1999; DeMarzo et al, 2003). Conversely, patients with GSTPi-positive breast cancer cells have shown to be resistant to treatment with chemotherapeutics, such as cyclophosphamide, methatrexate, adriamycin, doxorubicin, 5-fluorouracil, docetaxel or paclitaxel (Su et al, 2003; Arai et al, 2008; Yu et al, 2009). The results of these studies suggest that the GSTPi-positive cancer cells neutralise the cytotoxic effects of chemotherapeutic agents by a mechanism similar to that of their normal counterparts against carcinogens. Yet, GSTPi expression has been reported to be undetectable in cancer cells in high percent of cases of patients with primary invasive breast carcinoma (Esteller et al, 1998). These intriguing reports prompted us to identify other potential source of GSTPi expression in breast cancer tumour microenvironment-associated stroma, such as fibroblast. Such an investigation has not been reported. One of the major tumour microenvironment-associated stromal cells is referred to cancer-associated fibroblast (CAF), which has been recognised to have major roles in the progression of cancer, including that of breast cancer (Orimo et al, 2001; Shekhar et al, 2001; Desmouliere et al, 2004; Micke and Ostman, 2004; Nakagawa et al, 2004; Tang et al, 2004; Galie et al, 2005; Micke and Ostman, 2005; Sugimoto et al, 2005; Cat et al, 2006; Ide et al, 2006; Patocs et al, 2007). Here we present a report of a statistically significant association between the loss of GSTPi expression in breast cancer cells and the maintenance of its expression in vimentin/α-SMA-positive CAF in tumour microenvironment in paired cases of primary invasive breast cancer and corresponding axillary lymph node metastases.