Va. Palda et al., THE RISE OF TAMOXIFEN - TEMPORAL AND GEOGRAPHICAL TRENDS OF TAMOXIFENUSE IN ONTARIO, Breast cancer research and treatment, 43(1), 1997, pp. 33-41
Purpose: To describe the change in use of tamoxifen over time and acro
ss countries in Ontario. Methods: Data from the Ontario Drug Benefit (
ODB) plan, Census Canada, and the Ontario Cancer Registry (OCR) were c
ombined and analysed to determine rates of tamoxifen use for females o
ver 65 for each county and the province overall, by year. Rates were a
nalyzed by repeated measures ANOVA to determine significance of change
s over time. Consistency of tamoxifen use across counties was determin
ed by the Spearman rank correlation coefficient, and overall variation
between counties was described using three statistical techniques: Ch
i-square analysis, the extremal quotient (EQ), and the systematic comp
onent of variation (SCV). Results: The number of one-month tamoxifen p
rescriptions per incident case of breast cancer rose significantly fro
m 13.51 in 1985 to 20.54 in 1990 (p < 0.001) and to 34.06 in 1992 (p =
0.001). Viewed differently, the number of women over 65 receiving tam
oxifen prescriptions per incident case of breast cancer changed from 1
.91 in 1985 to 3.14 in 1990 to 4.54 in 1992. Statistically significant
variation in the rate of tamoxifen prescribing was demonstrated betwe
en Ontario counties in all three years by Chi Squared analysis (p < 0.
0001). Both the EQ and the SCV declined from 1985 to 1990, suggesting
more uniform prescribing across the province. Little change in overall
variation was seen between 1990 and 1992. All counties over time tend
ed to prescribe generic preparations more often and shifted from 10 mg
to 20 mg formulations. Conclusions: The significant increase in the r
ate of tamoxifen use and trend towards more uniform prescribing across
Ontario between 1985 and 1990 coincided with the publication of two i
mportant documents outlining the benefits of tamoxifen in early breast
cancer. Despite this trend, variation in tamoxifen use between counti
es remains. There has been little change in uniformity of prescribing
since 1990.