Purpose: We report long-term followup data on patients with World Health Organization (WHO) grade I bladder tumors, and determine whether histopathological subgrouping as papillary neoplasm of low malignant potential and low grade papillary carcinoma is of clinical value.
Materials and methods: All 680 patients in western Sweden with first diagnosis of bladder carcinoma in 1987 to 1988 were registered and followed for at least 5 years. Of the tumors 255 (37.5%) were stage Ta, WHO grade I. Tumors were further classified as papillary neoplasm of low malignant potential in 95 patients and low grade papillary carcinoma in 160 according to WHO and the International Society of Urological Pathology consensus classification of urothelial (transitional cell) neoplasms of the bladder.
Results: Mean age of patients at first diagnosis of low grade papillary carcinoma was 69.2 years, which was 4.6 years higher than those with papillary neoplasm of low malignant potential (p<0.005). During a mean observation time of 60 months our 255 patients underwent 577 operations for recurrences and had 1,858 negative cystoscopies. The risk of recurrence was significantly lower in patients with papillary neoplasm of low malignant potential compared to those with low grade papillary carcinoma (35 versus 71%, p<0.001). The risk of recurrence was higher in patients with multiple tumors at first diagnosis as well as those with recurrence at the first followup after 3 to 4 months. Stage progressed in 6 patients (2.4%), all with low grade papillary carcinoma at diagnosis.
Conclusions: More than 90% of patients with stage Ta, WHO grade I have a benign form of bladder neoplasm, and few have truly malignant tumors. Future research should focus on reducing the number of recurrences and followup cystoscopies, and finding methods to identify malignant tumors so that pertinent treatment can be instituted. Subgrouping of WHO grade I bladder tumors as papillary neoplasm of low malignant potential and low grade papillary carcinoma seems to add valuable prognostic information.