Cytokeratin 5/6 expression in pT1 bladder cancer predicts intravesical recurrence in patients treated with bacillus Calmette-Guérin instillation.

Bacillus Calmette-Guérin (BCG) instillation is the gold standard for the treatment of patients with pT1 bladder cancer but causes severe adverse effects. Few predictive factors have been established for intravesical recurrence and/or stage progression in bladder cancer. We analysed 138 patients who underwent transurethral resection of bladder tumour and were pathologically confirmed to have stage pT1 bladder cancer. Of these, 72 patients (52.2%) received intravesical BCG instillation, 12 patients (8.7%) demonstrated stage progression, and five patients (3.6%) died of the disease. The number of patients who received BCG instillation was more in the group with multifocal tumours than that in the group with unifocal tumours (p=0.0034). Among 53 patients (38.4%) who demonstrated cytokeratin 5/6 (CK5/6) expression, 15 patients (28.3%) showed CK5/6 expression in more than 10% of tumour cells and 38 patients (71.7%) showed CK5/6 expression in 1-10% of tumour cells. CK5/6 expression was observed in both invasive and non-invasive components in 15 patients (28.3%), only in invasive components in 30 patients (56.6%), and only in non-invasive components in eight patients (15.1%). Furthermore, CK5/6 expression was observed in tumour cells only in front of the invasive component and stroma in 24 patients. The proportion of CK5/6-expressing tumour cells in the invasive component was significantly higher than that in the non-invasive component (p<0.001). The follow-up period for patients who received BCG tended to be shorter than that in the non-BCG patients. The CK5/6-positive group displayed significantly shorter recurrence-free survival (RFS) than the CK5/6-negative group (p=0.0412). Importantly, CK5/6 expression was a significant predictive factor of inferior RFS in the BCG instillation group (p=0.0197). In contrast, CK5/6 expression was not significantly associated with RFS in the non-BCG instillation group (p=0.841). Thus, CK5/6 expression can be a predictive marker for RFS in patients with pT1 bladder cancer and can provide critical information for patient care.