However, the American Cancer Society suggests that some men should examine their testicles monthly, especially if they have a family history of cancer, and the American Urological Association recommends monthly testicular self-examinations for all young men.Symptoms may also include one or more of the following:

a lump in one testis which may or may not be painful
sharp pain or a dull ache in the lower abdomen or scrotum
a feeling often described as "heaviness" in the scrotum
firmness of the testicle
breast enlargement (gynecomastia) from hormonal effects of β-hCG
low back pain (lumbago) due to the cancer spreading to the lymph nodes along the backIt is not very common for testicular cancer to spread to other organs, apart from the lungs. If it has, however, the following symptoms may be present:

shortness of breath (dyspnea), cough or coughing up blood (hemoptysis) from metastatic spread to the lungs
a lump in the neck due to metastases to the lymph nodesTesticular cancer, cryptorchidism, hypospadias, and poor semen quality make up the syndrome known as testicular dysgenesis syndrome. Causes
A major risk factor for the development of testis cancer is cryptorchidism (undescended testicles). It is generally believed that the presence of a tumor contributes to cryptorchidism;  when cryptorchidism occurs in conjunction with a tumor then the tumor tends to be large. Other risk factors include inguinal hernias, Klinefelter syndrome, and mumps orchitis. Physical activity is associated with decreased risk and sedentary lifestyle is associated with increased risk. Early onset of male characteristics is associated with increased risk.
Over a lifetime, the risk is roughly 1 in 200 (0.5%). It is the 16th most common cancer in men. It accounts for less than 1% of cancer deaths in men (around 60 men died in 2012). Other animals
Testicular tumors occur also in other animals. In horses, these include interstitial cell tumors and teratomas. Typically, the former are found in older stallions (affected stallions may become extremely vicious, suggesting excessive production of androgen), and the latter are found in young horses and are large. References
External links

Ball Checker, self-exam app from the Testicular Cancer Society
Testicular Cancer – detailed guide from the American Cancer Society
Testicular Cancer – National Health Service information and resource page (UK)
Testicular cancer statistics from Cancer Research UK