PetEducation.com explains that calcinosis cutis is a condition in dogs that causes hard nodules to develop on the back or groin. Calcinosis cutis is caused by excessive treatments with corticosteroids or glandular tumors. Additional conditions that cause lumps on the back and body include hematomas and allergic reactions to insect bites.
According to WebMD, abscesses are common infections in dogs that can occur on the back and body. Abscesses are bacterial infections that present as painful, pus-filled lumps at the site of a bug bite or puncture wound. Epidermal inclusion cysts are firm lumps that can be found anywhere on the skin and can easily become infected. Epidermal inclusion cysts often contain matter that is cheesy in consistency.
PetMD adds that sebaceous cysts are superficial bumps in dogs that can develop anywhere on the body. Sebaceous cysts are benign and contain dead skin cells, sweat or clear fluid. Sebaceous cysts are caused by plugged oil glands and are most common in cocker spaniels. In many cases, sebaceous cysts rupture and heal on their own, but the cysts can also become chronic and infected. It is important for dog owners to consult with a veterinarian if their dogs experience chronic sebaceous cysts to remove and analyze the cysts.