S100A8 was sporadically detected as an unmodified proteoform:it was found in 4 SM patients and in 4 Ctrls but never in CM patients.Similarly, the hyperoxidized form of S100A8 was found in just 2 SMpatients and in 3 Ctrls, at very low levels, while nitrosylated S100A8was found at a higher frequency: in 1 CM patient, 8 SM patients, andin 3 Ctrls. Here, S100A8 is linked to systemic mastocytosis.