© Örjan Hallberg, Hallberg Independent Research 2010
Breast cancer cases are registered as left or right-sided in Sweden and many other countries. Figure 1 shows that breast cancer constantly since 1970 has been more prevalent on the left breast than on the right breast. A left laterality is clearly noticed.
Figure 1. Left laterality of breast cancer among Swedish women. From Hallberg, Johansson 2010 [1].
If the number of reported cases are accumulated over time the total left laterality in Sweden is around 7 %. See Figure 2.
Figure 2. Based on in total 200 000 cases of breast cancer since 1958 in Sweden the left laterality is around 7 %.
A similar analysis of the in total 1167 cases of breast cancer among men shows a left laterality of around 15 %. See Figure 3.
Figure 3. The left laterality of breast cancer among men in Sweden based on accumulated number of cases since 1971.
According to earlier studies regarding the laterality of melanoma, the same situation is seen in western type of countries, [2]. A closer look at Swedish data reviels that laterality data started to be registered as late as in 1999. Figure 4 shows that the left laterality of melanoma in Sweden seems to stabilize around 10 %.
Figure 4. The laterality of reported cases since 1999 around 10 % in Sweden.
Melanoma and breast cancer both have a left excess laterality of 10 % in Sweden. Since the left laterality of breast cancer among men is even higher, the explanation of breast feeding via the left breast as the main cause can be disregarded.