I am 32 with stage 4B MMMT of the uterus.
My cancer markers including my CA125 were all normal, with the exception of my HDL which was 385.
My oncologist said that this form of cancer does NOT have any readable cancer markers, unless it is in ovarian form, then the CA125 is helpful.
And because it is a mixed tumor, it can show up again anywhere. I've had to have bone scans and CT scans etc. I have no doubt that if they did some staining of the cells in her breast cancer, they would find cells that had MMMT characteristics.
If her MMMT is platinum resistant, then her oncologist should find another treatment option.