PAT-24 : Two Cases of Spindle Cell/Sclerosing Rhabdomyosarcoma Arising in Adults

Background: Spindle cell/sclerosing rhabdomyosarcoma (SRMS) is a variant of embyonal rhabdomyosarcoma, recently defined by WHO in 2013, and formerly classified as spindle cell rhabdomyosarcoma (SRMS). The prognosis is generally excellent. It represents 3 percent of all rhabdomyosarcomas. We will present two adult cases of SRMS with precise gene analysis. Case 1: A fifth decade female with past history of mandibular deformity anteriorly consulted a local medical doctor because of pain in the right mandibula. Case 2: An eighth decade male with unremarkable past history consulted a local medical doctor because of arthralgia of the left hip joint. Osseous tumor of the left ilium, subcutaneous tumor of the left sided nape, multiple pulmonary nodules, multiple osteopathy were pointed out. Cytological findings: Both showed tumorous proliferation of scattered spindle cells with oval nucleus can be seen. Chromatin pattern appear fine-granular. Irregularity of nuclear shape can be observed. In case 1, cigar-like nucleus can occasionally be seen. In case 2, dense cytoplasm, suggestive of differentiation for skeletal muscle, can be detected. Pathological diagnosis: Both show non-epithelial spindle cell tumorous proliferation, basically compatible with the cytological features mentioned as above. Immunohistochemical examination demonstrated myogenic origin and high MIB-1 labelling index. Gene analysis Case 1 PAX-FOXO1 (-), MYOD1 codon 122---mutation (+) Case 2 SYT-SSX (-), PAX-FOX01 (-) Discussion: In case 1, it is quite difficult to recognize the origin of the tumor cytologically, because of absence of characteristic cytoplasmic features of skeletal muscle. Typical nuclear shape, cigar-like, is the key to confirm the diagnosis cytologically.