According to Dogs Life, dogs can develop lumps for many reasons, including harmless processes that result in the deposition of excess fat cells or more dangerous conditions, such as cancer. Doctor Peter Green of Heathmont Animal Hospital states that the two most common causes of a lump on a dog’s rib cage are lipomas and sebaceous cysts. Lipomas are benign and harmless tumors, while sebaceous cysts result from blocked oil glands.
Dogs Life explains that most lipomas grow slowly. They may reach a certain size and then appear not to grow at all. Usually, such benign tumors range from the size of a pea to the size of an orange, but in exceptional cases, they may exceed 10 pounds. Lipomas do not cause dogs pain, but they can be removed if they interfere with a dog’s movement or quality of life. Surgical intervention is usually successful in removing these fatty growths.
Dogs Life warns that some of the potential causes of lumps on dogs are quite dangerous. Dogs should always be seen by a veterinarian when lumps are found, particularly if the lump bleeds or grows rapidly. In addition to metastatic tumors, dogs can also suffer from abscesses. Abscesses often result from grass seeds that stick to a dog's coat and eventually migrate under the skin.