causing autoimmune reactions. One example is sarcoid reactions that resemble sarcoidosis, a T cell-driven, multi-organ, granulomatous inflammatory disease. Sarcoid reactions might mimic cancer progression and can, as shown in this case, include skeletal lesions (which are rare in true sarcoidosis). This fact makes correct diagnosis extremely important. Misinterpretation of sarcoid reactions as progressive disease can cause psychological distress and unnecessary second-line treatments. Skin lesions, available to punch biopsy, often help in establishing the correct diagnosis. Sarcoid reactions subside with steroid treatment and by withholding checkpoint inhibition. Interestingly, sarcoid reactions tend to be associated with a good treatment response to immunotherapy.