title: Adherence to oral diabetes medications and glycemic control during and following breast cancer treatment.
abstract: OBJECTIVE
  We evaluated changes in oral diabetes mellitus medication adherence and persistence, as well as glycemic control for the year prior to breast cancer (BC) diagnosis (Year -1), during BC treatment, and in subsequent years.
  
  
  METHODS
  Cohort study of 4216 women diagnosed with incident early stage (I and II) invasive BC from 1990-2008, enrolled in Group Health Cooperative. Adherence was measured in prevalent users at baseline (N = 509), during treatment, and 1-3 years post-diagnosis using medication possession ratio (MPR), % adherent (MPR ≥0.80) and discontinuation rates. Laboratory data on glycosylated hemoglobin (HbA1c ) was obtained for the corresponding periods.
  
  
  RESULTS
  Compared with Year -1, mean MPR for metformin/sulfonylureas (0.86 vs 0.49, p < 0.001) and % adherent (75.3% vs 24.6%, p < 0.001) declined during BC treatment. MPR and % adherent rose slightly during Years 1-3 post-diagnosis but never returned to baseline. Discontinuation rates increased from treatment to Year +1 (59.3% vs 75.6%, p < 0.001) and remained elevated during subsequent observation periods. Compared with baseline, increased HbA1c (7.0% vs 7.4%, p = 0.001) and % women with high HbA1c >7.0% (34.9% vs 51.1%, p < 0.001) coincided with decreased adherence.
  
  
  CONCLUSIONS
  Diabetes mellitus medication adherence declined following BC diagnosis, whereas discontinuation rates were relatively stable but poor overall. The proportion of adherent users increased only marginally following treatment, whereas the proportion of women meeting goals for HbA1c decreased considerably. These data support the hypothesis that adherence and subsequent glycemic control are sensitive to BC diagnosis and treatment. Confirmatory studies in other settings, on reasons for reduced adherence post-cancer diagnosis, and on subsequent indicators of glycemic control are warranted.
authors.affiliation: Department of Epidemiology, University of Washington School of Public Health, Seattle, WA, USA; Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Calip
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Hubbard
authors.forename: Andy
authors.initials: A
authors.lastname: Stergachis
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: Malone
authors.forename: Julie R
authors.initials: JR
authors.lastname: Gralow
authors.forename: Denise M
authors.initials: DM
authors.lastname: Boudreau
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D001943:Breast Neoplasms / Q000097:blood / Q000453:epidemiology* / Q000628:therapy*; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy* / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D038321:Glycemic Index / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage*; D055118:Medication Adherence; D008875:Middle Aged; D013997:Time Factors; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents
keywords: breast cancer; diabetes mellitus; glycemic control; medication adherence; pharmacoepidemiology