The testicles contain numerous cell types that produce and support the development of sperm. Tumors of the testicle can originate from any of these cell types. Malignant (cancerous) tumors are often associated with cryptorchidism: testicles that fail to descend into the scrotum and remains in the abdomen. Pets with testicular tumors may have an obvious enlargement of the affected testicle. Some testicular tumors (i.e.: Sertoli Cell tumors) create hormonal imbalances and lead to feminization symptoms: milk production by the mammary glands, pattern hair loss, and attraction to other male dogs. Other testicular tumors (i.e.: interstitial cell tumors) do not cause enlargement of the testicle and are found incidentally during an ultrasound procedure. Fortunately, the majority of testicular tumors are slow to spread and can be cured with castration.