Necrosis is usually quite rare to absent in LGMPs of the urinary bladder (Figure 2, E).
In the LGMPs of the urinary bladder, there is significant immunohistochemical overlap between myofibroblastic proliferations diagnosed as IMT or PMP.
The pathologic differential diagnosis of bladder LGMPs is summarized in Table 2.
In 20 LGMPs listed in Table 1, previous urinary bladder instrumentation was ascertained, so that they were labeled as PSCN.
In fact, surgical management is a sign of the controversy surrounding the nature of LGMPs, the consequent limited workload of such lesions for a single surgeon, and the anecdotal and subjective judgments.
In fact, only a fraction of these cases (but a fraction that includes IMT, PMP, and PSCN cases) harbor ALK gene rearrangements with evidence of clonal proliferation, whereas the remaining LGMPs are either reactive or due to an unknown genetic abnormalities.
The LGMPs of the urinary bladder include different lesions extending from benign, pseudosarcomatous entities to low-grade, inflammatory fibrosarcomas, and they mainly affect patients in their middle decades.