During the worm’s normal development, a cell known as the anchor cell breaks through a structure called the basement membrane, which initially separates the uterus from the vulva.....
As far as I know, the basement membrane separates the skin cells from the underlying tissue. An epithelial cancer is considered invasive when it has breached the basement membrane, which gives it access to the underlying tissue and allows it to metastasize all over the body. Most skin cancers initially metastasize through direct extension. I don’t know where the author got the info that the basement membrane separates the uterus from the vulva. And this is in the very respectable Scientific American? To me, this makes the entire premise suspect. And just a side comment......I was in cancer detection for decades and came to the conclusion that the Group/Person funding any research project WILL get the result they desire. Sad, but true.
The article is probably trying to specify that the specific membrane in question in the worm is the one separating the uterus from the vulva.
I long ago realized that scientific topics written for lay people often leave out details whose lack makes the articles terribly uninformative and often nonsensical. This is why I no longer read scientific articles targeted at a lay audience.