TOPIC: Signs and Symptoms of Chest Diseases TYPE: Medical Student/Resident Case Reports INTRODUCTION: We present a patient who had localized chest pain for at least five years and was diagnosed with clear cell chondrosarcoma as an incidental finding on a chest roentgenogram obtained for reasons unrelated to his chest pain. CASE PRESENTATION: A 56-year-old male was seen in primary care for acute on chronic right breast pain. He had multiple prior encounters with atypical chest pain in the same area over the previous five years. He was referred for EKG and cardiac stress testing, which he never completed. Physical exam was notable for right gynecomastia and pseudo-folliculitis. No further evaluation was recommended; he was advised to use warm compresses. As part of a worker's compensation case after exposure to generator fumes, a chest roentgenogram demonstrated a right mid-lung zone partially calcified mass. CT chest revealed an expansile right fourth rib lesion near the costochondral junction measuring 9.8 cm x 7.4 cm. CT guided biopsy demonstrated a mesenchymal neoplasm with epithelioid cells and clear cells. Immunostaining was strongly positive for S100, vimentin, H3 K36M, and clusterin; ALK1 and CD138 negative. A definitive diagnosis could not be made, favored to be chondroblastoma with atypical features, although clear cell chondrosarcoma could not be excluded due to H3 K36M staining. He underwent successful chest wall resection and reconstructive surgery with negative tumor margins. Final pathology was clear cell chondrosarcoma based on the presence of clear cells and areas of invasion. Surveillance CT chest 9 months post-op was negative for signs of recurrence. DISCUSSION: Clear cell chondrosarcoma is a rare, low-grade bone sarcoma, occurring in 2-3% of all chondrosarcoma patients. It tends to involve long bones (90%) and the epiphysis as opposed to chondrosarcomas which involve the pelvis, hip, shoulder, metaphysis and diaphysis. Due to its low-grade activity and indolent course, diagnosis is often delayed a year or longer. It may be difficult to distinguish from chondroblastoma, but clear cell chondrosarcomas occurs mostly in older patients (3rd to 5th decade) as opposed to children and young adults (chondroblastoma). H3 K36M staining occurs primarily in chondroblastoma, but can occur in chondrosarcoma. The most common presenting symptom is localized pain. This patient's intermittent symptoms and missed diagnostic studies delayed his diagnosis, which would have been facilitated with a routine chest roentgenogram. Clear cell chondrosarcomas are notoriously resistant to chemotherapy and radiation; wide surgical resection represents definitive therapy. CONCLUSIONS: Clear cell chondrosarcoma is a challenging tumor to diagnose clinically and pathologically; immunostaining for H3 K36M may help. This case underscores the importance of chest radiography in evaluating any patient with chest pain. REFERENCE #1: Itälä, A., et al., An Institutional Review of Clear Cell Chondrosarcoma. Clinical Orthopaedics and Related Research®, 2005. 440: p. 209-212. REFERENCE #2: Bjornsson, J., et al., Clear cell chondrosarcoma of bone. Observations in 47 cases. Am J Surg Pathol, 1984. 8(3): p. 223-30. REFERENCE #3: Nakayama, R., et al., What Factors Are Associated with Treatment Outcomes of Japanese Patients with Clear Cell Chondrosarcoma? Clin Orthop Relat Res, 2020. 478(11): p. 2537-2547. DISCLOSURES: Speaker/Speaker's Bureau relationship with Boehringer-Ingelheim Pharmaceuticals Please note: $5001 - $20000 by Jaime Betancourt, source=Web Response, value=Honoraria Speaker/Speaker's Bureau relationship with Vapotherm, Inc Please note: $5001 - $20000 by Jaime Betancourt, source=Web Response, value=Honoraria Speaker/Speaker's Bureau relationship with Boehringer-Ingelheim Pharmaceuticals Please note: 2014-Present Added 04/21/2021 by Jaime Betancourt, source=Web Response, value=Honoraria Speaker/Speaker's Bureau relationship with Vapotherm, Inc Please note: 2019-Present Added 04/21/2021 by Jaime Betancourt, source=Web Response, value=Honoraria Advisory Committee Member relationship with Vapotherm, Inc Please note: 2020 Added 04/21/2021 by Jaime Betancourt, source=Web Response, value=Honoraria No relevant relationships by Christopher Miller, source=Web Response Stock Holder relationship with Merck Please note: $5001 - $20000 by Guy Soo Hoo, source=Web Response, value=Stock Holder Stock holder relationship with Amgen Please note: $5001 - $20000 by Guy Soo Hoo, source=Web Response, value=Stock Holder Stock Holder relationship with GlaxoSmithKline (GSK) Please note: $5001 - $20000 by Guy Soo Hoo, source=Web Response, value=Stock Holder Stock holder relationship with Pfizer Please note: $5001 - $20000 by Guy Soo Hoo, source=Web Response, value=Stock holder Stock holder relationship with XOMA Please note: $1001 - $5000 by Guy Soo Hoo, source=Web Response, value=Stock holder No relevant relationships by Caitlin Yumori, source=Web Response No relevant relationships by Jin Zhong, source=Web Response