Question special

I really enjoyed reading this paper. I was particularly interested in figures 3 (Number of apps by target cancer type) and 4 (Percent distribution of apps in comparison to estimated new cases of cancer, by gender, Canada 2013).
It's interesting that breast cancer comprises the vast majority of cancer-related apps at almost 50%. I wonder why colorectal, lung and prostate cancer comprise less than 10% of the apps even though they account for a significant percentage of new cancer cases in Canada.
Did you find any potential explanation for these results during your study?