Wearing a bra or tight clothing is not a great idea for healthy people without cancer. It promotes lymphatic back-up and toxin build up. However someone who has had cancer should not risk this added trauma to a damaged area.
After a mastectomy and reconstruction, you are always more prone to infection and damage, especially if you have had radiation. These tissues which have been so traumatized around the breast with tests, radiation, surgery, and possibly with implants do not need another battle to fight.
So ladies, throw away thoses bras. You don’t need to compromise your modesty. Wear camisoles under your tops. Just be sure to cut any elastic which may constrict.
The great thing after reconstruction is that you no longer sag. What possible reason would there be for post mastectomy patients to ever wear a bra? To hide your scarred breasts? Well if you get an infection, your breasts will have even more scars. Plus, it is only reasonable to assume based on the evidence in the paper linked below that recurrence or metastis are more frequent with constriction of lymphatic and blood flow.
Bras were invented by someone in the fashion industry to line their pockets. Leave constrictive clothing behind and be kind to your body.
(The above link is to an article that provides the references and research to back up these claims.)