非浸潤性乳頭状尿路上皮癌における軽微な高悪性度成分は、より緩慢な挙動と関連がない

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.

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.

Those findings suggest that pTaHGs with minor HGc do not exhibit more indolent behaviour and should be approached similar to pTaLGs.