Can an epididymal cyst turn cancerous?

Epididymal cyst. Epididymal cyst is a benign cyst and does not turn into cancer. It might grow though and in that case it might cause some testicualr discomfort. Regular exams (twice a year) is the way to follow it up.
Yes, but rarely. Has it been confirmed by histology (microscopic exam of the tissue?
No, but... I have never heard or read any discussion on such concern in my 45-yr study and practice in urology. Theoretically, cancerous change can be a concern, but very unlikely; as stated, I have never heard or read.... For individual concern, ask and talk with Doc timely.
Unheard of. Sebacious cysts never turn cancerous. There is a rare type of cancer called sebacious carcinoma that has a similar presentation to sebacious cyst, but it's very rare (however, I have one patient like that).