Lumps that you see on the skin of your dog are commonly associated with tumors, a term that has become interchangeable with cancer. The reality is that all lumps and bumps are not tumors, and all tumors are not cancerous. Physical examination only reveals the presence of a lump and beyond that everything else is just guess work. Even veterinarians know nothing about them unless they perform a biopsy or examine an aspirate under a microscope.
Sometimes a small anatomically normal sac, especially one containing fluid, is mistaken for a tumor. Cocker Spaniels, for example, are predisposed to develop such sacs known as sebaceous cysts. Caused by the plugging of oil glands in the skin, skin cysts may be comprised of dead cells, sweat or fluid. More often than not, these cysts rupture by themselves and disappear. If irritated or infected, these have to be removed and sent for pathological examination just to be sure about the type of infection. Sebaceous cysts can potentially develop into tumors, medically known as sebaceous adenomas. Adenomas are benign tumors that do not present a major health risk and are easily excised.
Tumors are formed when cell starts dividing and multiplying uncontrollably and eventually form a mass. This pathological process is known as neoplasia. Benign tumors do not have the capacity to invade and spread and are usually encircled by fibrous tissue. They do not present any major health risk unless they compress upon neighboring organs. Most benign tumors can be excised and the matter is forgotten.
Cancerous or malignant tumors are a major health risk. The initial mass that forms is the primary tumor from which cells can break off and form secondary tumors in other parts of the body, a process called metastasis. Cancer that spreads or has the capacity to spread to distant organs is known as metastatic cancer.
Malignant tumors are known by the type of tissue they originate from. Carcinomas arise from epithelial (lining) tissue and sarcomas from connective tissue. Different types of malignant tumors are usually named using carcinoma and sarcoma as a suffix to define the basic characteristic of cancer in dogs. The prefix indicates the location of the tumor. For example, canine hepatocarcinoma refers to dog liver cancer. Similarly, pancreatic cancer in dogs is a malignant growth of tumors known as adenocarcinomas, which refers to a tumor originating in glandular epithelium.
Cancer treatment in dogs depends largely upon the location of the tumor and the stage to which it has advanced.