Gene expression studies have previously identified only KRT5 mRNA and not KRT6 isoforms in normal breast and basal-like breast cancer in humans [11, 21, 51]. Consequently in normal breast tissues and cancer, the K5/6 antibody is thought to target only K5 . We found LP-9 peritoneal cells to express KRT6C but not KRT5. We confirmed that K6 protein is expressed in ovarian cancer cell lines and LP-9 cells but only faint K5 bands could be detected with K5/6 in OVCAR-5, OV-90 and SKOV-3 cell extracts. The low expression of K5 protein in ovarian cancer cell lines was confirmed by immunofluorescence as only 10–15% of ovarian cancer cells had detectable K5 protein without carboplatin treatment (see Figure 5C and 5D). The observed molecular weights of K5 (56 kDa) and K6 (52 kDa) were close to the predicted molecular weight of K5 (62 kDa) and K6 (60 kDa), respectively, and consistent with previous studies that have observed K5 at 56 kDa in rat liver cancer  and K6 at 50 kDa in bladder cancer .