Statistical comparisons of the expression of the genes between subtype I and IV showed significant differences in the expression of folate receptor alpha (FOLR1) (Figure 9) with no differences for SLC19A1, FPGS or DHFR. The reduced expression of FOLR1 might have contributed to the poor response of subtype IV breast cancer to the methotrexate-containing CMF regimen. Here, FOLR1 is linked to breast carcinoma.