I don’t imagine that happens a lot. Most women who get breast cancer are older than their 30s when they get it. And what if a woman was in remission and had a good prognosis? You never know what will happen or who will get sick or when. A woman who’s been healthy her whole life might have a baby and then come down with an illness a year later, while the breast cancer survivor never has a recurrence.
Many breast cancers are steroid-dependent. A woman who has had this type of breast cancer and has a good prognosis significantly worsens her prognosis by having another baby, because of the elevated circulating steroid levels during pregnancy. The timing of this 66 year old’s breast cancer, originally diagnosed soon after the birth of the twins, is probably not a coincidence — it was most likely triggered by the pregnancy, or at least accelerated by the pregnancy (i.e. maybe she was going to get it anyway, but she probably wouldn’t have gotten it by age 69 if it hadn’t been for the pregnancy). The same principle applies to much younger women who are already at high risk due to a previous bout of breast cancer.
I’m just pointing out that if a story was posted on FR about a woman in her thirties who already had a couple of children, who had recently had breast cancer with a poor prognosis for 5 year survival, and who was now choosing to have yet another child, it’s likely that no one would post a reply accusing her of being “selfish” for choosing to have another child, even when she knew she was unlikely (statistically much MORE unlikely than this 66 year old was) to live to see her child start kindergarten.