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atypical intradermal smooth muscle neoplasm

Wednesday 1 June 2016

atypical intradermal smooth muscle neoplasms; AISMN; formerly "cutaneous leiomyosarcomas"

Definition: Atypical intradermal smooth muscle neoplasms (AISMN, formerly known as cutaneous leiomyosarcomas) are uncommon neoplasms, which seem to be remarkable for their excellent prognosis in contrast to their deeper counterparts.


- superficial cutaneous leiomyosarcoma

- Malignant dermal spindle cell neoplasm with giant cells & SMA+ consistent with AISMN (cutaneous leiomyosarcoma)

Atypical or mitotically active dermal smooth muscle neoplasms are uncommon lesions, which are most often termed "cutaneous leiomyosarcoma," although preexisting-mostly small-series suggest a low risk of aggressive behavior.

In a 2011 series (21358302), there was a striking male-to-female preponderance (4.3:1), with a mean age of 56 years (range, 6 to 82y). Nine patients had a history of malignancies (6 of the skin). Tumors measured 1.3 cm on average and were predominantly located on the trunk (32) and lower extremities (30).

Histologically, all tumors are confined to the dermis or showed only very superficial, focal subcutaneous extension. The majority show an infiltrative growth pattern with fascicles of atypical eosinophilic spindle cells ramifying between dermal collagen fibers. Primary tumors show a mean mitotic rate of 4.7/10 high-power fields.

By the Fédération Nationale des Centres de Lutte Contre le Cancer grading system, 97% of primary tumors were grade I lesions, with only 3% showing necrosis.

All tumors are immunopositive for smooth muscle actin; 98% expressed desmin, 90% caldesmon, and 45% pankeratin (usually focal).

Follow-up in 52 cases (mean, 51 mo) showed no metastases or tumor-related deaths. Eighteen tumors showed local recurrence at a mean interval of 43 months; 12 of the recurrent lesions showed positive margins in the primary excision and 1 showed margins @<@0.2 cm. Margin status was not available for the other 5 cases, which recurred locally. (21358302)

Recurrent tumors showed, on average, 13.7 mitoses/10 high-power fields. Of recurrences, 47% were grade I lesions, 35% were grade II, and 18% were grade III, and 28% showed necrosis. (21358302)

The primary excision of tumors, which later recurred, showed no difference in grade, presence of necrosis, or mitotic rate, compared with those that did not recur; there were no discernible clinical differences either.

These tumors, when confined to the dermis or showing only minimal subcutaneous involvement, seem to carry no evident risk of metastasis; hence, the designation "sarcoma" could be inappropriate. The term "atypical intradermal smooth muscle neoplasm" have been proposed.

Margin status is the most important predictor of recurrence. On excision with clear margins, the risk of local recurrence is very low. (21358302)

AISMN can have significant morphologic variation and overlap with other spindle cell neoplasms of the skin and that a limited panel of key immunohistochemical stains should be used to distinguish this lesion.

The different surgical measures such as wide excision versus Mohs procedure showed a similar clinical outcome.

Molecular biology

- PTEN alteration (22448121)

  • Although the significance of frequent PTEN loss supports a molecular mechanism of tumor genesis, the diagnostic utility of the stain remains to be determined.

See also

- cutaneous smooth muscle tumors

Open references

- Classification, molecular characterization, and the significance of pten alteration in leiomyosarcoma. Grossmann AH, Layfield LJ, Randall RL. Sarcoma. 2012;2012:380896. doi : 10.1155/2012/380896 PMID: 22448121 (Free)


- Atypical intradermal smooth muscle neoplasms (formerly cutaneous leiomyosarcomas): case series, immunohistochemical profile and review of the literature. Hall BJ, Grossmann AH, Webber NP, Ward RA, Tripp SR, Rosenthal HG, Florell SR, Randall RL, Cockerell CJ, Layfield LJ, Liu T. Appl Immunohistochem Mol Morphol. 2013 Mar;21(2):132-8. doi : 10.1097/PAI.0b013e31825f4af2 PMID: 22820664

- Atypical intradermal smooth muscle neoplasms: clinicopathologic analysis of 84 cases and a reappraisal of cutaneous "leiomyosarcoma". Kraft S, Fletcher CD.
Am J Surg Pathol. 2011 Apr;35(4):599-607. doi : 10.1097/PAS.0b013e31820e6093 PMID: 21358302