"There have been reports that, because of the harmful effect of radiation on the heart, postmastectomy radiotherapy may worsen survival – due to acceleration of ischaemic heart disease. 3046 Danish women at high risk of breast-cancer recurrence were randomly assigned to receive: drugs (chemotherapy or tamoxifen, depending on whether they were postmenopausal or not) or drugs-plus-radiotherapy. The women were followed-up over the next ten years. Out of the 1521 women who did not receive radiotherapy, 799 of them died from breast cancer and 13 from ischaemic heart disease. Out of the 1525 women who received radiotherapy, 674 women died from breast cancer and 12 from ischaemic heart disease. "
I think its a randomised trial, because they did randomly assign patients to receive different treatments.
But the long follow up makes me wonder if it could be a prospective co-hort study.
100s of personal statements examples here