Malignancy-Associated Sarcoid-Like Reaction in a Case of Triple-Negative Breast Cancer on F-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography

Sarcoidosis is a type of chronic granulomatous disease that is characterized by a widespread development of noncaseating granulomatous lesions in multiple organ systems. When a patient has lesions with noncaseating epitheloid cell granulomas without the systemic symptoms of sarcoidosis, it is termed as a sarcoid-like reaction.[1] Thus, differentiating the two conditions based on histopathology alone is not possible. Studies suggest that sarcoidosis may precede, occur concurrently as paraneoplastic syndrome or follow hematological and solid malignancies.[23] Very few studies have described the occurrence of sarcoid-like reactions following breast cancer and have attributed it as a paraneoplastic syndrome.[4] Sarcoid-like reactions can occur in close proximity to the tumor as an immunological response to the tumor antigens.[5] Antineoplastic treatment such as chemotherapy has been found to induce or cause a flare-up of malignancy-associated sarcoid-like reaction.[26] Surprisingly, in our patient, the sarcoid-like reaction mimicked the malignant lesions' response to chemotherapy, which raised questions about the previously known course of this condition [Figure 1]. In such cases, to avoid misdiagnosis or overtreatment, such as unnecessary chemotherapy for presumed residual/recurrent metastases, histopathological evidence may be necessary.[7] Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) may be used to identify the suspicious lesions and guide the site of biopsy. No specific treatment is recommended in malignancy-related sarcoid-like reactions.[18] Through this case, we hope to describe one of the courses of sarcoid-like reaction, which has not been well documented in literature, and highlight the potential role of F-18 FDG PET/CT in its evaluation.

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Figure 1 F-18 FDG PET/CT was performed on a 54-year-old female patient with triple-negative breast cancer for initial staging and for response assessment to chemotherapy six months later. Her baseline PET/CT showed metabolically active primary lesion in the left breast parenchyma (a: arrowhead, c: thin arrow) with metastasis to ipsilateral axillary lymph nodes (a: black arrow). Metabolically active mediastinal lymph nodes (a: solid white arrow, c: solid white arrow) and parenchymal nodules in bilateral lungs were also noted. Histopathological examination of endobronchial ultrasound-guided aspirate from mediastinal lymph nodes showed numerous nonnecrotizing epitheloid cell granuloma (e) in a background of reactive lymphoid cells. This led to a diagnosis of malignancy-associated sarcoid-like reaction. post-chemotherapy scan showed metabolically active primary lesion (b: arrowhead, d: thin arrow) in the left breast as well as the previously noted axillary lymph nodal metastases (b: black arrow). These lesions showed a significant reduction in size and metabolic activity suggestive of partial response. In addition, the previously noted mediastinal lymph nodes (b: solid white arrow, d: solid white arrow) also showed a reduction in size and metabolic activity, although to a lesser extent when compared to the other lesions. FDG PET/CT: Fluorodeoxyglucose positron emission tomography/computed tomography

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