Sarcoid is thought to develop in predisposed individuals by a cross-reaction to tumor, bacterial, viral, or inorganic antigens or immunogenes. Patients respond by forming noncaseating granulomas, which are most commonly intrathoracic. Sarcoid-like reaction (SLR) refers to the development of noncaseating granulomas in patients who do not fulfill the criteria for systemic sarcoidosis.
In oncological patients, SLR most commonly occurs in the lymph nodes draining a malignant tumor, but can also be observed in the organ of tumor origin and distant tissues. It develops after antineoplastic treatment with biologic modifiers (e.g., interferon and interleukin-2), single or combination chemotherapy agents, or even after surgery without chemotherapy.
The patient above has a history of melanoma of the left lower extremity with recurrent ipsi- and contra-lateral inguinal nodal involvement that has been treated with surgery (most recently 8 months ago) and chemotherapy in the remote past (cisplatin, vinblastine, and dacarbazine). The PET from 3 months ago (left panel) was clear. The new PET (right panel) shows new supraclavicular (red arrow), intra-thoracic (yellow arrows), and upper abdominal (blue arrow) adenopathy. The lymph nodes are highly FDG-avid and most prominent in the chest, where we see the symmetric hilar and mediastinal adenopathy typical of sarcoid and would be atypical for nodal involvement from lower extremity melanoma. It is important to keep SLR in mind in order to avoid over-calling disease progression. This can be more problematic in cases of intrathoracic neoplasms that would be expected to recur in the chest and involve hilar and mediastinal lymph nodes. Symmetrical hilar involvement can be a helpful hint in these cases.
- Inoue K, Goto R, Shimomura H, Fukuda H. FDG-PET/CT of sarcoidosis and sarcoid reactions following antineoplastic treatment. Springerplus. 2013 Dec;2(1):113.
- Tchernev G, Tana C, Schiavone C, Cardoso JC, Ananiev J, Wollina U. Sarcoidosis vs. Sarcoid-like reactions: The Two Sides of the same Coin? Wien Med Wochenschr. 2014 Jul;164(13-14):247-259.