Okay, let's unpack some of the steps in that...
Breast Cancer is more common among women who defer having children to later in life, or who never have children. In the US, intentionally deferring children is a behavior seen most commonly among professional women. Professional women have greater household income than others. So that's the first unpack: "breast cancer is associated with wealth". This is why the two largest hot-spots of breast cancer in the US are Marin County in California and Long Island in New York.
Again sticking to the US, multi-lingualism is generally seen in two groups.
The first is obvious: immigrants. Immigrants are a mix of lower-income labor from nearby countries[1], and higher-income professionals from across the globe looking to get better-paying jobs or opportunity. So without any evidence to back me up, I'm going to just assert that immigrants are in the middle of the income scale.
The second group of multi-linguals in the US are the rich. Either the college-educated who took language in school or those who travel enough to use another language. Again, in aggregate, the college-educated are on the higher end of the income spectrum. Those who travel, in aggregate, tend to be wealthier with disposable income that they can spend on experiences like travel.
So yeah, there's plenty to argue with in the second part of my thesis ("multi-lingualism is associated with higher-wealth"), but I think it's a pretty good bet.
[1] It's hard to a low-income laborer to get enough money to travel to a country far away