In a patient who had childhood sarcoma treated with surgery and chemotherapy but without radiation, would this history impact their risk of second malignancy from radiation to a new cancer given as an adult?  

Absolutely. Recent data from SJLIFE suggests that the cumulative incidence of developing any subsequent cancer can still be high among patients treated without radiotherapy, if the patient is a carrier for known mutations characterized by a well established monogenic cancer risk with high-low penetr...