Radiation and hormonal therapy may lead to penile shortening.

Prostate cancer treatment may shorten penis – Yahoo! News

NEW YORK (Reuters Health) – Men who receive
combination treatment with hormone therapy plus radiation for local or
locally advanced prostate cancer may experience a significant reduction in
penile length, according to a report in the January issue of the Journal
of Urology

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It has been long suspected that men may develop penile shortening after surgery, but this is the first report that I am aware of that it can also happen after radiation.