[521] Atypical Intradermal Smooth Muscle Neoplasms: Clinicopathologic Analysis of 85 Cases

S Kraft, CDM Fletcher. Brigham and Women's Hospital, Boston, MA

Background: Atypical or mitotically active dermal smooth muscle neoplasms are commonly termed “cutaneous leiomyosarcomas”. However, preexisting - mostly small - series of these rare lesions suggest a low risk of aggressive behaviour.
Design: 85 cases were retrieved from the authors' consult files and institutional files. H&E sections were examined, immunohistochemistry was performed, and clinical details were obtained from referring physicians.
Results: There was a striking male to female preponderance (4.3:1), with a mean age of 56 yr (range 6-82, with 91% ≥40). 9 patients showed a prior history of malignancies (6 of the skin). Tumors measured 1.3 cm in average (11 tumors ≥2.0 cm) and were predominantly located on the trunk (32) and lower extremities (31). The remainder occurred on the upper extremities (17) or head & neck (4). Histologically, all tumors were either confined to the dermis or showed only very superficial subcutaneous extension. The majority showed an infiltrative growth pattern with fascicles of atypical spindle cells ramifying between collagen fibers. Necrosis was present in 10%. All cases showed cytologic atypia. Primary tumors showed a mean mitotic rate of 6/10 HPF. Recurrent tumors showed 14/10 HPF (and a greater degree of cytologic atypia). All tumors were immunopositive for SMA; 98% expressed desmin, 90% caldesmon, 27% pan-keratin (focal or scattered), and 1 focally S-100. Follow-up ranged from 5-156 months (mean 47). No metastases or tumor-related deaths were observed. Local recurrences were observed in 18 cases. All recurrences had developed prior to consultation, after a mean interval of 43 months. No recurrences were observed after consultation (mean follow-up of 32 months). 13 of the recurrent lesions showed positive margins in the primary excision and 3 showed margins <0.2 cm. Margin status was not available for 2 cases. The primary excisions of tumors which later recurred showed no increase in cellular atypia, presence of necrosis, or mitotic rate when compared to those which did not recur, nor were there any discernible clinical differences.
Conclusions: These tumors show a strong male predilection and predominantly occur on the trunk and lower extremities. When confined to the dermis or showing only minimal subcutaneous involvement, they appear to carry no risk of metastasis, hence the designation “sarcoma” is inappropriate. Margin status is the most important predictor of recurrence. Upon excision with clear margins, the risk of local recurrence is absent or very low. Hence we propose the term “atypical intradermal smooth muscle neoplasm”.
Category: Dermatopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 103, Wednesday Afternoon


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