Over expression of metallothionein predicts resistance of transitional cell carcinoma of bladder to intravesical mitomycin therapy

PURPOSE: Metallothionein, a low molecular weight intracellular protein, binds mitomycin with high affinity protecting the tumor DNA. We prospectively studied the relationship of metallothionein expression in bladder transitional cell carcinoma and resistance to intravesical mitomycin. MATERIALS AND METHODS: A series of 45 consecutive patients with superficial transitional cell carcinoma treated with intravesical mitomycin were studied. Resected tumor tissues were stained with metallothionein monoclonal antibody E9. Two pathologists scored staining intensity and distribution. All patients were followed with regular flexible cystoscopy. RESULTS: Median patient age was 73 years (range 44 to 89). Tumor grade was 1 to 3 in 6, 33 and 6 cases, respectively. In 20 patients (44.44%) tumor recurred after mitomycin therapy. Median cytoplasmic staining scores for recurrent and nonrecurrent tumors were 5 (range 0 to 61) and 0 (0 to 14), respectively. Median nuclear staining scores for recurrent and nonrecurrent tumors were 3 (range 0 to 56) and 0 (0 to 11), respectively. Median followup of patients without recurrence was 18 months (range 12 to 36). Nuclear and cytoplasmic staining scores were significantly higher in recurrent than in nonrecurrent tumors. There was no significant relationship of metallothionein expression with tumor grade. CONCLUSIONS: Over expression of metallothionein predicts the resistance of bladder transitional cell carcinoma to intravesical mitomycin therapy.