How does cancer affect my pet?

How does cancer affect my pet?

The most obvious symptom of most cancers is a lump that continues to enlarge. This lump may ulcerate, bleed or cause other physical effects (pressure, displacement, etc.) on the surrounding tissues.

Benign cancers only enlarge in a local area by uniform, smooth expansion but malignant cancers may invade the surrounding tissues with "tentacles" or irregular projections (i.e. "cancer the crab"). In fact, pathologists use these differences in growth habit to help decide if the cancer is benign or malignant. Malignant neoplasia may also be malignant because it spreads widely through the body. Widespread distribution of a cancer may occur by "direct seeding", which occurs when cancer cells break away from the original tumor and seed in body cavities (such as the pleural cavity of the chest or peritoneal cavity of the abdomen). Malignant cancer may also be spread when cancer cells invade the blood, which then carries tumor cells to distant tissues where the cells lodge and start new tumor masses (metastases). The most common sites for metastatic cancer to develop are the liver, the lungs and the lymph nodes, although other sites can be affected.

Weight loss due to loss of body fat and muscle is common in malignant cancer and unexplained weight loss can be an important sign of malignancy.

A few tumors induce clinical signs that are not readily explained by local or distant spread of the tumors. These are known as paraneoplastic syndromes. Some syndromes are due to abnormal hormone production by the cancer. (Hormones are internal secretions that pass into the blood and stimulate other organs to action.) Examples of paraneoplastic signs and symptoms include loss of hair, increase or decrease in blood glucose levels, and increased blood calcium levels.