Cysts, warts, infected hair follicles, hematomas (blood blisters) and others do cause concern and can create discomfort for the dog, though non-cancerous lumps have less health impact than cancerous growths.
Cancerous growths can be either malignant or benign, and occasionally even share characteristics of both. Malignant lumps tend to spread rapidly and can metastasize to other areas of the body. Benign growths tend to stay in the place of origin and do not metastasize; however they can grow to huge proportions (see such an example of inoperable tumor pictured on the right).
Mammary gland tumors, mast cell tumors, cutaneous lymphosarcoma, malignant melanoma, fibrosarcoma and many other types of tumors with truly scary names command respect and diligent attention on the part of dog owners and veterinarians.
Below are the most common methods of finding out "what it is" …
Some ulcerated masses lend themselves to easy cell collection and identification by having a glass microscope slide pressed against the raw surface of the mass. The collected cells are dried and sent to a pathologist for staining and diagnosis. Sometimes the attending veterinarian will be able to make a diagnosis via the smear; otherwise, a specialist in veterinary pathology will be the authority regarding tumor type and stage of malignancy.
Many lumps can be analyzed via a needle biopsy rather than by total excision. A needle biopsy is performed by inserting a sterile needle into the lump, pulling back on the plunger, and "vacuuming" in cells from the lump. The collected cells are smeared onto a glass slide for pathological examination. Usually the patient isn’t even aware of the procedure. Total excision of the mass is attempted if the class of tumor identified warrants surgery.
Superficial lumps and bumps do not require that CT Scans be done, so this procedure is usually reserved for internal organ analysis. If a superficial malignant tumor is diagnosed, however, a CT Scan can be helpful in determining if metastasis to deeper areas of the body has occurred.
As with CT Scans, X-ray evaluation is generally reserved for collecting evidence of internal masses. Most lipomas are superficial and reside under the skin or skeletal muscles. There are other lumps that can be palpated by the veterinarian via manual examination; however, the extent and origin of that mass will often be best revealed via CT Scanning.