Bilateral Upper Arm Granulomas Induced by Leuprorelin Acetate Injection Mimicking Malignant Soft Tissue Tumors: A Case Report.

Leuprorelin acetate is a common anticancer medication used for prostate cancer treatment. One of the local adverse reactions after leuprorelin injection is the development of reactive granulomas, typically presenting as subcutaneous nodules. In this case report, we describe a 73-year-old patient with prostate cancer who developed unusually large sized intramuscular reactive granulomas, which mimicked malignant soft tissue tumors. The patient, who had been receiving leuprorelin acetate treatment for the past 12 months, noticed painful masses in both upper arms. Based on the findings of magnetic resonance imaging and fluorodeoxyglucose-positron emission tomography/computed tomography, a diagnosis of malignant soft tissue tumor was strongly suggested. However, further investigation through needle biopsy ultimately led us to the final diagnosis of reactive granuloma. The masses spontaneously resolved after discontinuation of leuprorelin injection. While reactive granulomas after leuprorelin injections are not rare, intramuscular cases are relatively uncommon. Despite using imaging studies as a rational initial approach in the diagnostic process, as we did in our case, their results turned out to be indistinguishable from those of malignant soft tissue tumors, thus highlighting the importance of pathological examination in confirming diagnosis, especially when a patient presents with atypical clinical manifestations.