Updated treatment response criteria for indolent systemic mastocytosis (ISM) were proposed by the European Competence Network on Mastocytosis (ECNM) and the American Initiative in Mast Cell Disease (AIM) based on discussions at a meeting in Vienna, Austria.

Their recommendations were published in The Journal of Allergy and Clinical Immunology: In Practice and focused on assessing symptoms and signs in patients before and during treatment. Grading and the definitions of different treatment response criteria were also proposed.

“The primary goal of ISM treatment is symptom reduction and improvement of mastocytosis-related [quality of life (QoL)] impairment,” the authors said. “Cutaneous, [gastrointestinal (GI)], and neurological symptoms, musculoskeletal pain, and the presence of skin lesions, anaphylaxis, and osteoporosis are the main drivers of disease burden in ISM and should be assessed in all patients, before initiation and over the course of treatment.”

To assess the primary symptoms of ISM, including skin itching and flushing, GI issues, musculoskeletal pain, and neurological symptoms, 3 patient-reported outcome measures (PROMs) were recommended: the mastocytosis symptom assessment form (MSAF), the mastocytosis activity score (MAS), and the ISM symptom assessment form (ISM-SAF).

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Outside of these PROMs, simpler criteria for symptom assessment could be applied, such as the grading system provided by the European Union/United States consensus group, which grades symptoms based on the need for treatment, the efficacy of therapy, and the need for hospitalization.

For clinical trials investigating the impact of ISM on QoL, 2 ISM-specific tools were recommended—the Mastocytosis Quality-of-Life Questionnaire MC-QoL and the similarly named Mastocytosis Quality-of-Life Questionnaire MQLQ.

Treatment response grading recommendations were also proposed by the ECNM-AIM consortium. They recommended that complete response be defined by an improvement of greater than 90%, major response be an improvement of greater than 60%, partial response be between 30% and 60%, and no response (NR) be used for less than 30% improvement.

The consortium mentioned that laboratory values, such as serum tryptase levels and KIT D816V allele burden, and histological findings, such as numbers of mast cells found in biopsies of bone marrow, skin, GI tract, or other affected organs, were limited in their usefulness as outcome parameters because they did not directly measure the severity of signs and symptoms or the level of QoL impairment. 


Pyatilova P, Akin C, Alvarez-Twose I, et al. Refined treatment response criteria for indolent systemic mastocytosis proposed by the ECNM-AIM consortium. J Allergy Clin Immunol Pract. 2022;10(8):2015-2024. doi:10.1016/j.jaip.2022.05.037