Tumors of the Penis and Prepuce
Dr. Douglas Brum
A complete physical examination with careful examination of the prepuce and penis is always the first step in diagnosing these masses. The entire length of the penis should be exposed by retracting the prepuce and extending the penis. Once this is complete, the entire surface of the penis can be observed for any potential tumors.
CBC. The CBC evaluates the red and white blood cells. If there is significant bleeding associated with a tumor, anemia may occur. Low red blood cell counts indicate anemia. Elevations in the white blood cell count may indicate infection.
Biochemical profile. The biochemical profile evaluates the metabolic status of a variety of organ systems. Since tumor development is more likely to occur in older animals (except for TVT), and since a surgical procedure is anticipated, a profile is a useful screening test to rule out other problems and or associated disease. Liver and kidney function are evaluated. Blood sugar and electrolytes are also checked to provide a good overall assessment of the general condition of the patient.
A urinalysis and culture are sometimes advised if a secondary urinary tract infection is suspected. The urinalysis is also a good test to evaluate the status of the kidneys in an older animal.
Chest x-rays are needed to check the lungs for any evidence of tumor spread prior to surgery. In older animals, it is also a good pre-operative screening test to evaluate for evidence of cardiac disease or other lung conditions. Abdominal X-rays are useful in evaluating the size and shape of other abdominal organs. Occasionally, with metastatic disease, the sublumbar lymph nodes, which are located under the vertebrae of the lower back, may be enlarged and visible radiographically.
The aspiration of a mass is usually a very good method of obtaining a sample of the tumor for identification. The collected cells are then examined microscopically (cytology) and checked for evidence of malignancy. A fine needle aspirate is generally a safe and effective method of tissue evaluation, but sometimes it is not diagnostic, since only a small number of cells are collected.
Occasionally, an impression smear can be made with some masses that are either ulcerated or friable by simply touching a microscope slide to the surface of the tumor. Cells from the tumor are transferred to the slide, where they can be evaluated microscopically. Since no needle insertion is needed, it is generally well tolerated by the patient. Unfortunately, most tumors require aspiration for the collection of cells for analysis.
A biopsy provides the best sample, as a core of tissue is obtained for histopathology, or microscopic examination of tissue. Biopsy usually provides more accurate information since a larger amount of tissue can be evaluated. Many times the biopsy is combined with the full removal of the entire tumor, called an excisional biopsy. Based on the previous diagnostics, it is not always needed to biopsy a tumor prior to its removal.
Most dogs with preputial tumors are asymptomatic and feel fine. Often the tumors are found incidentally on a routine physical examination. When found, attempts to characterize the tumor should be made, so the best decision for the patient may be made. After taking the appropriate diagnostics steps, if the preputial mass has the potential to cause problems, that is if it is malignant or is causing discomfort, it should be removed.
If the mass appears benign, and the dog is asymptomatic, other issues should be addressed. For example, if the patient is a poor anesthetic candidate for other reasons, it may be more prudent to postpone surgery and observe the tumor for changes. This decision must be discussed with your veterinarian, and the potential problems from not removing the tumor weighed carefully against anesthetic risk. On the other hand, tumors of the penis almost always cause some type of problem and necessitate removal. Specific treatment for tumors of the penis and prepuce include:
Surgical removal of the tumor. Surgery is generally the treatment of choice for most tumors, except TVT. The surgeon attempts to remove the entire tumor and tries to get "clean surgical margins," which implies removing a small amount of normal tissue surrounding the mass along with the tumor in an attempt to leave the remaining tissue free of tumor cells. Depending on the results of the biopsy, surgical excision may be curative. Occasionally, with penile tumors, it may not be possible to remove the entire mass without removing the entire penis (penile amputation).
Chemotherapy. Depending on the type of tumor, chemotherapy may be considered. Chemotherapy may be quite effective with some tumor types, but less effective with others. Chemotherapy is the treatment of choice with TVT. The drug vincristine is given intravenously once a week, usually for 2 to 7 treatments. Vincristine treatment usually provides an excellent response with generally minimal side effects. Chemotherapy for other tumor types is generally not nearly as effective, and usually is combined with surgical excision.
Radiation therapy. Radiation therapy is also effective as a single mode of treatment for TVT. Radiation therapy may also be used if the tumor is too large for removal. Palliative radiation therapy may decrease the tumor size and relieve some clinical signs in sensitive tumors. Radiation therapy may also be recommended postoperatively based on the biopsy of the removed tumor. Mast cell tumors and squamous cell carcinomas are two of the more common tumor types that are radiosensitive.