What is the risk of breast cancer that you quote to young women with early stage Hodgkin's lymphoma receiving involved field/site radiation therapy?

The risk depends on many different factors, including the amount of breast exposure to radiation, age of the patient, chemotherapy regimen, etc. Patients at greatest risk are likely those with axillary involvement who are < 30, where a large portion of their breast maybe unintentionally irradiated. Due to the omission of elective nodal irradiation of the uninvolved axilla with the use of IFRT from Mantle field, there has been a significant reduction in breast cancer development in HL survivors.

Interestingly, Conway et al IJROBP 2017 reported on 10 year survivors of Hodgkin lymphoma treated with chemotherapy alone, < mantle field, and mantle field radiation using the British Columbia Cancer registry. The 20 year risk of breast cancer was 2.2...