Radiation-Induced Myonecrosis Presenting as a Subcutaneous Mass After Combined Modality Therapy for Non-small Cell Lung Cancer

Abstract

A 60-year-old African-American man with a long history of tobacco smoking presented with a lung nodule detected incidentally on a chest radiograph in November 2004. Computerized tomography (CT) confirmed the presence of a 5 3-cm mass in the left upper lobe with mediastinal lymph node involvement (T2 N2 M0). CT-guided biopsy findings were consistent with squamous cell carcinoma. He received four cycles of paclitaxel (175 mg/m) and carboplatin (area under the curve 5) along with thoracic radiation to the left upper lobe mass and mediastinum on a q 3-week cycle. The radiation dose prescription was 7000 cGy to the planning target volume delivered in 200-cGy daily fractions using 6-mV beams. The dose to the isocenter within the target volume was 7350 cGy (Figure 1). The dose was prescribed using lung density corrections. A four-field beam arrangement was used consisting of anterior-posterior, posterioranterior, left posterior oblique, and right anterior oblique beams. The patient tolerated the concurrent chemoradiation well. He did experience esophagitis (grade 2) toward the end of the radiation treatment, which was treated symptomatically. Overall, he had a partial response based on the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Six months later, the patient developed pain and swelling in his upper back. On physical examination, he had mild tenderness over the left paraspinal region. There was a vague nodular swelling in the upper mid back in the field of radiation. A CT scan of the chest revealed an ill-defined low attenuation lesion within the left trapezius muscle lying medial to the left scapula at the level of the fifth and sixth ribs without invasion of the underlying ribs or the adjacent scapula grossly (Figure 2). This area of abnormality corresponds to the 5000-cGy radiation isodose line in Figure 1. An ultrasound of the lesion revealed thickening with contour abnormality in the musculature corresponding to the area of the abnormality seen on the previous CT examination. This region was hyperechoic compared with normal muscle. This region was adequately visualized by sonography, and a biopsy was performed. This biopsy demonstrated findings of skeletal muscle with marked necrosis and fibrosis but no evidence of malignancy. A fluorodeoxyglucose positron emission tomography scan prior to the biopsy did not reveal any uptake in this lesion. A repeat CT-guided biopsy of the soft tissue mass revealed only benign-appearing epithelial cells with scattered elongated nucleoli, probably representing fibroblasts. There were no features diagnostic for malignancy. A follow-up evaluation 4 months later showed spontaneous resolution of the mass (Figure 3). Given the lack of uptake on the emission tomography scan, three negative biopsies, and spontaneous resolution, it was deemed consistent with radiation myonecrosis. The patient has subsequently been followed more than 15 months without any evidence of recurrence.