STUMPs, a pathology apart

STUMPs are tumors that cannot be formally classified as benign or malignant tumors.

The histoprognostic criteria validated by WHO 2003 are the presence or absence of tumor necrosis*, nuclear atypia**, mitotic index***.

The diagnosis of STUMP is retained when the smooth muscle tumor presents:
•true tumor necrosis
•one of the two criteria and the second is difficult to assess:
• presence of diffuse moderate to severe atypia and a mitotic index difficult to assess or “borderline” between 8 and 9 mitoses/10 hpf
•presence of moderate to severe atypia and necrosis whose tumoral or ischemic nature is difficult to assess
•myxoid or epithelioid cell smooth muscle tumors with nuclear atypia, 2 to 5 mitoses/10 hpf.

The diagnosis of leiomyosarcoma is made when two of these three criteria are present.

Benignity is retained when one of the three criteria is present, with the exception of necrosis; it is then a variant of leiomyoma (benign myoma).

It is generally not possible to have the diagnosis before the intervention and the anatomopathologic examination.

We are therefore faced with a "suspicious" or "atypical" myoma which requires the same initial care as a suspicion of sarcoma: re-reading and discussion of the file in an expert center, first complete excision without fragmentation. The diagnosis must always be confirmed by a peer review or at least an expert. (the list of specialized centers is given on the website www.netsarc.sarcomabcb.org; Institut Curie, certified European expert center is one of them: Dr S Bonvalot, www.curie.fr).
One should not “overtreat” a benign lesion or “undertreat” a true sarcoma.

There is generally no additional treatment, but prolonged clinical and radiological follow-up for several years.