Cancer heterogeneity and its biologic implications in the grading of urothelial carcinoma

Urothelial carcinoma of the bladder often contains areas with different histologic grades. The influence of cancer heterogeneity on grading and its relation to patient outcome is uncertain.

The study group consisted of 164 patients with Ta urothelial carcinoma diagnosed at the Mayo Clinic between 1985 and 1986. None had previous or coexistent urothelial carcinoma in situ or invasive carcinoma. The primary (most common) and secondary (second most common if at least 5% of the cancer) patterns of cancer growth were graded by the newly proposed World Health Organization and International Society of Urological Pathology (WHO/ISUP) grading system. Scores of 1, 2, and 3 were assigned to urothelial neoplasms of low malignant potential (LMP), low grade urothelial carcinoma, and high grade urothelial carcinoma, respectively. The mean follow-up was 7.7 years (range, 0-13.3 years; median, 9.2 years). Progression was defined as the development of invasive carcinoma, distant metastasis, or death due to bladder carcinoma.

Patient ages ranged from 36 to 96 years (mean, 69 years), and the male-to-female ratio was 4:1. Disease progression developed in 32 patients during a mean follow-up of 7.7 years. The mean interval from diagnosis to progression was 3.1 years (range, 0.01-8.7 years). Progression free survival was 82%, 77%, and 76% at 5, 7, and 10 years, respectively. Primary and secondary grades were different for 52 patients (32%). Based on the worst grade, 19 patients (12%) had urothelial neoplasms of low malignant potential (LMP), 92 (56%) had low grade carcinoma, and 53 (32%) had high grade carcinoma. Histologic grades based on worst, primary, secondary, and combined primary and secondary grades were all significant for predicting progression (P = 0.0009, 0.0004, 0.001, and 0.0001, respectively). Seven-year progression free survival rates for patients with LMP, low grade, and high grade carcinoma (based on worst grade) were 93%, 82%, and 61%, respectively; for patients with combined scores of 2, 3, 4, 5, and 6, survival rates were 93%, 80%, 82%, 68%, and 40%, respectively. The difference between patients with combined scores of 5 or 6 was statistically significant (P = 0.02).

Histologic grade of urothelial carcinoma based on the newly proposed WHO/ISUP grading system stratifies patients into prognostically significant groups. Grading should also take cancer heterogeneity into consideration, and prognostic accuracy appears to be increased when the combined primary and secondary grades are applied. [See editorial counterpoint on pages 1509-12 and reply to counterpoint on pages 1513-6, this issue.]