Table 1.

Response assessment criteria for this retrospective study ECD = Erdheim–Chester disease. Physicians performed objective clinical response assessments. Metabolic responses required comparison between nuclear positron emission tomography (PET)-generated images, with the use of positron emission tomography response criteria in solid tumors (PERCIST). Serial comparison was conducted between either computed tomography (CT) or magnetic resonance imaging (MRI) using RECIST 1.1 criteria (response evaluation criteria in solid tumors) when applicable. SUL = standardized uptake by lean body mass, TLG = total lesion glycolysis.

Response Assessment Tool	Most Utilized in	Stable Disease (SD)	Partial Response (PR)	Complete Response (CR)	Progressive Disease (PD)
Clinical	Localized ECD	Grossly unchanged by serial physical examination and/or serial photoimaging or laboratory values	Grossly regressed by serial physical examination and/or serial photoimaging	Grossly resolved by serial physical examination and/or serial photoimaging	Grossly enlarged from prior baseline by examination and/or serial photoimaging
PERCIST [17]	Disseminated disease by PET	Not meeting other criteria	>30% decrease (minimum 0.8 units) in SUL peak	Normalization of all lesions to an SUL equal to surrounding tissue and mean in liver	>30% increase (minimum 0.8 units) in SUL peak or >75% TLG increase in the 5 highest metabolically active lesions
RECIST 1.1 [18]	Disseminated, visceral disease or neurologic disease by CT and/or MRI	Not meeting other criteria	Sum ≥30% decrease in diameter of target lesion	Complete disappearance of any target lesions	Sum ≥20% increase in diameter of target lesion