Are all metachronous multifocal urothelial carcinoma created equal?

Metachronous multifocal urothelial carcinoma could theoretically result from intraluminal seeding implantation (monoclonal), pan-urothelial field change (oligoclonal) or mixed mechanisms (1). While not completely elucidated, different potential mechanisms might impact clinical behavior, course, biological characteristics and eventually the response to intravesical Bacillus Calmette-Guérin (BCG), especially when comparing primary and subsequent non-muscle-invasive bladder cancer (NMIBC) after radical nephroureterectomy for upper urinary tract urothelial carcinoma (UTUC).