Mixed high and low grade bladder tumors--are they clinically high or low grade?

The pathological grade of bladder cancer has an immense impact on patient treatment and prognosis. While most bladder tumors show pure high or low grade patterns, some show a mixed pattern. We explored the incidence and clinical significance of this phenomenon.

A total of 642 patients with a mean age of 67.5 years underwent transurethral resection of nonmuscle invasive bladder tumors between June 1998 and December 2008, including 156 and 454 with low and high grade lesions, respectively. In 32 patients (5%) mixed grade tumors were found, defined as low grade tumors with 10% or less of a high grade component. All patients were followed a median of 60 months postoperatively.

Mean age, the proportion of men and the proportion of stages Ta/T1 in patients with mixed grade tumors were between those of the high and low grade groups. Five-year recurrence-free survival was similar for high, low and mixed grade tumor types (56.9%, 63.8% and 66.4%, respectively, p=0.252). Five-year progression-free survival was significantly lower in patients with high grade disease (73.9%, p<0.0001) but similar in those with high and mixed grade tumors (99% and 96.9%, respectively, p=0.167). Similarly, disease specific survival was significantly worse in patients with high grade tumors (p<0.0001) but similar in those with high and mixed grade lesions (p=0.679).

Mixed grade is found in about 5% of nonmuscle invasive tumors, representing a patient group with unique clinical features. The clinical course of patients with mixed grade tumors parallels that of patients with low grade tumors.