A study on effectiveness of screening mammograms

Background So far, no randomized controlled trials with a mean mammographic screening interval of greater than or equal to2 years has demonstrated sta tistically significant mortality reduction for women younger than age 50. T he issue of screening frequency is vital in detection of primary breast can cer. Methods The study group consisted of cancers diagnosed in women who partici pated in a serial screening programme with a mean screening interval of 2 y ears. To study the effectiveness of the screening, a comparison is made bet ween the distribution of age at which the tumour could be detected when bie nnial mammographic screening is the only detection method, and the distribu tion of age at which the tumour would be detected by either biennial mammog raphic screening or the development of symptoms. Some recently developed st atistic methods, such as bootstrap, the maximum likelihood distribution est imator for doubly censored data and the EM algorithm, are used in estimatio n of these distributions. Results The hypothesis tests and confidence intervals show that the differe nce between the two distributions was statistically significant for women y ounger than 50 and 50-70 years old, but not for women over 70 years. Conclusions The statistical analysis indicates that for women younger than 50, and 50-70 years of age, a screening mammogram every other year is not f requent enough to detect primary breast cancer, but for women over 70 years , it might be sufficient.