Abstract
AIMS: The latest WHO edition proposed using a cut-off of ≥5% high-grade component (%HGc) as a criterion to label non-invasive papillary urothelial carcinomas as high-grade (pTaHG). It also suggested that tumours with minor high-grade component behave more indolently and are better labelled as mixed low- and high-grade papillary carcinomas. METHODS AND RESULTS: We investigated the prognostic value of %HGc along with other clinical and morphological parameters. 130 pTaHGs and 96 pTaLGs were included. 9% and 12% of pTaHGs had ≤5% and ≤10% HGc, respectively. Anaplasia was present in six cases (5%), necrosis in 18 cases (14%) and CIS in 5 cases (4%). On average, the highest mitotic count per 1 HPF was 2.4 (range = 0-18), and the mean number of mitoses per 10 HPF was 9 (range: 0-93). The mean tumour diameter was 2.1 cm. Tumour multifocality was observed in 32 cases (25%). Among the histological parameters, only mitotic activity showed a correlation with the %HGc (P < 0.001). While recurrence was not significantly different between pTaLGs and pTaHGs (25% vs 35%; P = 0.09), stage progression was significantly different (0% vs 8%; P = 0.005). The two parameters that were associated with recurrence in pTaHGs were tumour multifocality and BCG therapy, while none was associated with progression. %HGc ≤5% and ≤ 10% did not correlate with lower rates of recurrence nor progression. CONCLUSIONS: Those findings suggest that pTaHGs with minor HGc do not exhibit more indolent behaviour and should not be approached similar to pTaLGs. [Correction added on 13 April 2026, after first online publication: This version changes the preceding sentence from "should be approached" to "should not be approached".].