LAUSR

Objectives To report 4 pediatric RMS in Guatemala [age range 8-13 years] exhibiting aggressive clinical behavior. Findings 2 cases involved sinonasal & paranasal sinuses; one the anterior mandibular facial area & another affecting paraorbital and mid facial region, with previous additional history of radiation therapy & R. ocular exenteration at 2 years of age for retinoblastoma. Rapid, massive growth with nasal obstruction was observed in all 3 cases, leading to gross. R. ocular displacement and facial deformity was noted in one case, while facial and mandibular swelling was reported in another. The period of tumor growth ranged from 2 -6 months. 3/ 4 patients were treated with Rad. & chemoth. & 1 patient (post radiation) also underwent surgical intervention as chemoth. & Rad. showed no response. Follow-up period ranged from 2 months to 3 years, where 2 patients were alive & disease free while the other 2 expired of wide spread disease, including CNS invasion & both patients within that cohort had evidence of regional lymph node metastasis and one of the 2 also exhibited CNS involvement. Histomor-morphologic subtypes included 3 embryonal and 1 post radiation subtypes. All cases reacted positively with IHC to desmin & myogenin. Ki67 labeling was 75% to 90 % in 3 cases and was not performed in the 4th. One of the cases which encompassed small round cell morphology also reacted positively with CD99, albeit with co-expression of desmin and myogenin. Conclusions Our cases highlight the aggressive nature of RMS, with distant metastasis in 3 cases and high Ki-67 labeling. Positive expression of CD99 should not deter from the diagnosis of RMS provided co-expression of myogenin and desmin is confirmed. Considering its aggressiveness and failure to respond to any form of current treatment, post-radiation RMS should be classified as an unspecific variant of RMS.