You seem to be suffering from Peyronie's disease.
Peyronie's disease is caused by scar tissue which forms along the length of penis in the corpora cavernosa.
The underlying cause of Peyronie's Disease is not well understood, but is thought to be caused by trauma or injury
to the penis.In your case cancer surgery
could have triggered the development of this problem,although calcium channel blockers and beta blockers have also been blamed for this problem.
A urologist can diagnose the disease and suggest treatment.
If there is mild pain or if there is no problem in intercourse,then nothing is done.However if there is pain in intercourse,a corrective surgery can be performed.
can provide conclusive evidence of Peyronie's disease.
Consult a urologist