Development of symptom-focused outcome measures for advanced and indolent systemic mastocytosis: the AdvSM-SAF and ISM-SAF ©

Background Advanced systemic mastocytosis (AdvSM), indolent systemic mastocytosis (ISM), and smoldering systemic mastocytosis (SSM) are rare diseases characterized by neoplastic mast cell infiltration of more than one organ. A content-valid patient-reported outcome (PRO) questionnaire that assesses relevant signs and symptoms that are important and understandable to individuals with a condition is critical for assessing new treatment benefit as well as supporting product labeling claims. Notably, no such PRO questionnaire has been developed in accordance with regulatory and scientific guidelines for use in AdvSM, ISM, and SSM patient populations. To fill that gap, this study documents the development and content validity of instruments evaluating signs and symptoms of systemic mastocytosis. Methods A review of peer-reviewed literature, advice meetings with clinical therapeutic area experts, patient concept elicitation interviews, concept selection and questionnaire construction meetings, and patient cognitive debriefing interviews were conducted, and regulatory feedback was incorporated. Results For AdvSM, 26 sign- and symptom-level concepts were identified in literature, 39 by clinicians, and 33 by patients. For ISM/SSM, 38 sign- and symptom-level concepts were identified in the literature, 39 by clinicians, and 57 by patients. Two patient-reported instruments, the Advanced Systemic Mastocytosis Symptom Assessment Form (AdvSM-SAF) and Indolent Systemic Mastocytosis Symptom Assessment Form (ISM-SAF)(©Blueprint Medicines Corporation), were developed based on consolidated findings. Cognitive debriefing interviews with AdvSM and ISM patients showed the AdvSM-SAF and ISM-SAF were understood and interpreted as intended by the majority of patients. Conclusion The AdvSM-SAF and ISM-SAF are content-valid tools measuring symptoms from AdvSM and ISM patients’ perspective.