Lower Back Pain in an Elderly Man With a History of Localized Prostate Cancer

A 70-year-old man with a history of localized prostate cancer treated with whole-pelvis radiation therapy with a boost to the prostate, in conjunction with androgen deprivation therapy 7 years prior, presented with lower back pain. A bone scan revealed an area of activity in the sacrum. What is the most likely diagnosis?
Source: Cancer Network - Category: Cancer & Oncology Source Type: news