12th May 2024

A 72-year-old man presents with lower back pain, difficulty urinating, and a decrease in urinary stream strength.

A 72-year-old man presents with lower back pain, difficulty urinating, and a decrease in urinary stream strength. His medical history is significant for hypertension and elevated prostate-specific antigen (PSA) levels noted during annual check-ups. A digital rectal examination reveals an enlarged, firm prostate. A bone scan indicates osteoblastic lesions in the pelvic bones and the lumbar spine. A biopsy of the prostate confirms adenocarcinoma.

Which is the most likely route by which this tumour spread to the pelvic bones?