Cats spayed after 2.5 years of age have a risk or incident rate 7 times higher than cats spayed before the first cycle. Most tumors occur in cats 9-11 years of age and are found primarily in the breasts closer to the tail. Can produce estrogen, which is the most severe effect of the tumor, causing liver and bone marrow damage. Often curable if caught early or chemotherapy may be needed. In cats with high estrogen levels surgery can be risky.
Neutering is preventative.
Also, this tumor can cause urinary tract blockage, weakness, pain, bleeding from the penis, and weight loss. Spreads to areas inside the pelvis and sometimes other organs. There is no treatment effective towards a cure but neutering may slow growth of the mass. This tumor is rarely seen in castrated males, neutering considered preventative.