Melanotic Schwannoma (MS): A ClinicoPathologic Study of 32 Cases
Jorge Torres-Mora, Mitual Amin, Andrew L Folpe. Mayo Clinic, Rochester, MN; William Beaumont Hospital, Detroit, MI
Background: MS, variably associated with Carney Syndrome (CS), are rare tumors that usually involve spinal nerve roots but may occur in other locations. Clinicopathological evaluation poorly predicts the behavior of MS. Fewer than than 200 cases have been reported. We report a series of 32 well-characterized MS, the largest series to date.
Design: 32 MS were retrieved and evaluated for growth pattern, nuclear atypia, cellularity, mitotic rate, and necrosis. Follow-up was obtained. Immunohistochemistry (IHC) for S-100 protein, melan A, HMB 45, tyrosinase, INI-1, glial fibrillary acidic protein (GFAP) and Ki-67 antigen was performed using commercially available antibodies and the Dako Envision detection system. Fisher's Exact Test was used for statistical analysis.
Results: The tumors occurred in 15 males and 17 females (mean age 42 years, range 11-84 years). Tumors occurred in paravertebral nerve roots (N=27), mediastinum (N=2), 5th cranial nerve, buttock, and cerebellum (N=1 each). No patient had a definite history of CS although 1 patient also had a cutanteous myxoma and is presumed to have CS. IHC was S100 protein (16/20, 80%), Melan A (18/20, 90%), HMB45 (20/20, 100%), tyrosinase (20/20, 100%), GFAP (0/20, 0%), and INI1 (retained in 20/20, 100%). Ki-67 index was <5% (18/20, 90%) and 5-10% (2/20, 10%). Clinical follow-up (19/32, 59%, mean 5.4 years, range 1 month-25 years) showed local recurrences in 7/19 (36%) and metastases in 9/19 (47%) patients. Metastastic sites included lung, pleura, liver, lymph nodes, leptomeninges, brain and soft tissues. The only feature that correlated with metastases was mitotic rate >2/10 high powered fields (p=0.03). Patients were alive without disease (N=8), alive with disease (N=7) and dead of disease (N=4).
Conclusions: Our study confirms the unpredictable and potentially aggressive nature of MS, with local recurrences and distant metastases in 36% and 47% of patients, respectively. The presence of elevated mitotic activity may help to predict those patients at greater risk for the development of metastases. A subset of MS lack S100 protein expression, an unusual finding in a neoplasm of putative schwannian origin. Although previous studies have clearly shown an increased incidence of MS in patients with CS, many MS occur in patients not known to have this syndrome. On-going evaluation of MS for loss of the CS-associated PRKAR1A tumor suppressor gene and DNA microarray study should help to clarify the relationship of MS to CS and to other melanocytic/nerve sheath tumors, respectively.
Category: Bone & Soft Tissue
Monday, March 19, 2012 1:00 PM
Poster Session II # 12, Monday Afternoon