A combination of distribution- and anchor-based approaches determined minimally important differences (MIDs) for four endpoints in a breast cancer scale.
OBJECTIVE
To determine distribution- and anchor-based minimal important difference (MID) estimates for four scores from the Functional Assessment of Cancer Therapy-Breast (FACT-B): the breast cancer subscale (BCS), Trial Outcome Index (TOI), FACT-G (the general version), and FACT-B.


METHODS
We used data from a Phase III clinical trial in metastatic breast cancer (ECOG study 1193; n=739) and a prospective observational study of pain in metastatic breast cancer (n=129). One third and one half of the standard deviation and 1 standard error of measurement were used as distribution-based criteria. Clinical indicators used to determine anchor-based differences included ECOG performance status, current pain, and response to treatment.


RESULTS
FACT-B scores were responsive to performance status and pain anchors, but not to treatment response. By combining the results of distribution- and anchor-based methods, MID estimates were obtained: BCS=2-3 points, TOI=5-6 points, FACT-G=5-6 points, and FACT-B=7-8 points.


CONCLUSIONS
Distribution- and anchor-based estimates of the MID do show convergence. These estimates can be used in combination with other measures of efficacy to determine meaningful benefit and provide a basis for sample size estimation in clinical trials.
Eton
David T
DT
Evanston Northwestern Healthcare and Northwestern University, Feinberg School of Medicine, 1001 University Place, suite 100, Evanston, IL 60201, USA. d-eton@northwestern.edu
Cella
David
D
Yost
Kathleen J
KJ
Yount
Susan E
SE
Peterman
Amy H
AH
Neuberg
Donna S
DS
Sledge
George W
GW
Wood
William C
WC
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000188:drug therapy / Q000534:rehabilitation*; D017326:Clinical Trials, Phase III as Topic; D004812:Epidemiologic Methods; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D010147:Pain Measurement / Q000379:methods; D011788:Quality of Life; D016896:Treatment Outcome