Most common tumour in undescended testis is :

Approximately 95% of testicular tumors are derived from germ cells. Seminomas tend to remain localized in the testis for a longer period, are radiosensitive, and metastasize to lymph nodes, whereas nonseminomatous neoplasms metastasis sooner, are radioresistant, and tend to metastasize hematogenous routes. Risk factors for development of testicular neoplasms Cryptorchidism (i.e., undescended testicle). Syndromes with testicular dysgenesis (e.g., Klinefelter syndrome). Family history and history of a tumor in the contralateral testis. Ref : Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 17. Pathology of the Male and Female Reproductive Tract and Breast. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds),Pathology: The Big Picture.