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The authors conclude that LMS-UB occurs in older adults of either sex and is characterised by aggressive behaviour, with adverse outcome in >60% of cases. Certain advantages of the FNCLCC system may support its more widespread adoption for future studies.

Mesenchymal tumors harboring GLI1 gene abnormalities are a rare but distinctive group of neoplasms whose clinicopathologic features are currently evolving. In particular, examples of this tumor with ACTB‐GLI1 gene fusion, tentatively termed ACTB‐GLI1 epithelioid mesenchymal neoplasm (EMN), show a distinctive monomorphic round‐to‐epithelioid morphology, nested to trabecular pattern of growth, and S100+/SOX10−/SMA– immunophenotype. We report the first case of this entity arising exclusively in the skin. A 69‐year‐old man with no prior history of neoplasia presented with a 1.5‐cm raised lesion on the left buttock. Histopathologic examination revealed a diffuse dermal proliferation of small, monomorphic, round‐to‐ovoid cells with hyperchromatic nuclei, focally enlarged nucleoli, and minimal eosinophilic to clear‐staining cytoplasm. These cells were arranged in confluent nests and trabeculae in a background of fibrocollagenous to focally myxoid stroma. Immunohistochemical analysis revealed strong positivity for S100 and CD56, and negativity for SOX‐10, SMA, Melan‐A, HMB‐45, and a variety of other markers. Based on the morphology and immunophenotype, molecular studies were performed, which revealed the presence of an ACTB‐GLI1 fusion transcript, confirming the diagnosis. Given the morphologic overlap of this tumor with other cutaneous round cell neoplasms and its potential for malignant behavior, ACTB‐GLI1 EMN is an important entity for pathologists to recognize.

Pleomorphic fibromas are rare benign cutaneous neoplasms associated with deletion/loss of chromosomes 13q and 17p, where RB1 and TP53 are located, respectively. Herein, we report five cases of pleomorphic fibroma arising in patients with germline TP53 mutations, suggesting a potential link with Li‐Fraumeni syndrome. All three patients were female and young (mean age 27) with a strong personal and/or family oncologic history and confirmed pathogenic germline TP53 mutations. In two patients, multiple pleomorphic fibromas were diagnosed. Clinically, the lesions arose at various cutaneous sites and were small (≤2 cm) and raised (4/5). Histopathologically, the tumors were paucicellular, composed of atypical spindled to stellate cells with hyperchromatic and variably pleomorphic nuclei. Mitotic activity was exceedingly low, although rare atypical mitotic figures were seen in one case. Immunohistochemically, the tumor cells were diffusely positive for p16 (3/3) and showed loss of Rb expression (5/5). All cases showed aberrant p53 expression (overexpression in 4, complete loss in 1). The tumors have followed a benign clinical course with no evidence of progression or recurrence. In conclusion, the development of multiple pleomorphic fibromas in a young patient may be a clue to an underlying genetic cancer syndrome involving TP53.