Tumors of the Penis and Prepuce in Dogs

Overview of Tumors of the Canine Penis and Prepuce

Tumors of the penis are rare in the dog, but preputial tumors are more common. Tumors that occur on the prepuce are similar to the tumors that grow on other haired regions of the body. Some of the most common preputial tumors include mast cell tumors, squamous cell carcinomas, papillomas, and fibromas.

The most common penile tumors are transmissible venereal tumors (TVT). Other tumors, including squamous cell carcinoma and adenocarcinomas, occur much less frequently but have been reported. Primary tumors of the urethra, especially transitional cell carcinomas, may occasionally extend into the penis.

Penile and preputial tumors typically occur in older dogs, with the exception of a transmissible venereal tumor. Transmissible venereal tumors are contagious and are spread by direct contact.

Boxer dogs seem to have a higher incidence of skin tumors than most dogs. Dogs at risk for transmissible venereal tumors include breeding animals or intact male dogs allowed to roam freely.

What to Watch For

Many dogs with preputial tumors are not symptomatic. If signs are present, they usually include:

• A mass or swelling on the penis or prepuce
• Discharge (occasionally bloody) from the prepuce or penis
• Excessive licking of the penis
• Foul odor
• If the tumor is causing a compressive lesion or blockage of the urethra, dogs may strain to urinate and become quite ill.

Diagnosis of Tumors of the Penis and Prepuce in Dogs

• A complete physical examination
• Complete blood count (CBC)
• Biochemical profile
• Urinalysis with or without culture
• Chest and abdominal radiographs (x-rays)
• Impression smear of a penile mass
• Biopsy of the mass
• Aspiration (inserting a needle and syringe into the tissue and obtaining a small sample of cells) and cytology (microscopic analysis of the cells) of the mass

Treatment of Tumors of the Penis and Prepuce in Dogs

• Surgical excision
• Chemotherapy
• Radiation therapy

Home Care and Prevention

Watch the incision daily for any sign of swelling or discharge. If skin sutures are used, they should be removed in 7 to 10 days. If your dog begins to lick the area excessively, an Elizabethan collar designed to prevent licking at incisions may be required. Seek veterinary care if your dog has a fever, is feeling ill post-operatively, is straining to urinate or seems painful when urinating.

If treating TVT, limit exposure to other dogs until the tumor has regressed. If chemotherapy is being used, periodic blood tests will need to be checked.

Animals should be re-evaluated periodically for signs of recurrence. The only tumor where preventive measures may help is TVT.

An excellent preventive measure is to have your dog neutered at an early age. Do not allow dogs to roam freely.

In-depth Information on Canine Tumors of the Penis and Prepuce

Tumors that involve the prepuce of the dog are similar in type and biologic behavior to tumors found elsewhere on a dog’s skin. Most of these tumors are not causing clinical problems for the dog at the time of their discovery. Occasionally they may ulcerate, bleed, itch or cause discomfort, and require more immediate attention, but usually ,they are found incidentally on routine examinations by veterinarians or by their owners.

Tumors of the penis usually cause more clinical signs, in general, and are more uncomfortable. Masses on the penis are irritating and cause excessive licking of the area. Some tumors (especially TVT) may be quite friable (small pieces may break off), and bleeding may be seen. Secondary infections may also be associated with penile tumors, often producing a foul smell. If the tumor is located near the urethral opening, the flow of urine may be inhibited, leading to straining to urinate. If the blockage is severe enough a urinary obstruction could occur, leading to an emergency situation and potential kidney damage. Fortunately, this is a rare occurrence.

The most common penile tumor is TVT and is the tumor that is mostly preventable. TVT is transmitted as tumor cells break off from the main tumor and are transplanted into susceptible tissue. Dogs contract TVT this way through sexual contact with infected dogs or from licking and smelling the tumors. It is for this reason that dogs will often have transmissible venereal tumors on their nose or lips. Neutering animals and decreasing exposure to stray dogs will help decrease its incidence significantly.

Other diseases that may cause similar clinical signs as tumors of the penis and prepuce include:

• Normal penile erection. A normal erection may be misinterpreted as a tumor if one is not familiar with the normal canine anatomy. The dog has a gland in the base of his penis (bulbus glandis) that swells, and becomes a hard spherical swelling. It is often confused with a penile tumor the first time it is seen.
• Urethritis and cystitis are inflammatory conditions of the urethra, which is the tubular structure that carries urine from the bladder through the penis, and bladder. Both conditions may cause discomfort, straining to urinate, discharge from the penis and excessive licking.
• Prostatic disease can also cause a penile discharge that can be bloody. A rectal exam should always be done to evaluate the size and shape of the prostate.
• Balanoposthitis is inflammation of the penile and preputial surface. This is a fairly common but not serious condition present in intact male dogs. Dogs with the problem may have a large amount of discharge from the penis, and lick the area excessively.
• Infected wounds or dermatitis on the prepuce may occasionally appear as ulcerated swellings on the surface of the prepuce, and might be confused with preputial tumors.

In-depth Information on Diagnosis

• 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.

In-depth Information on Therapy

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.

Follow-up Care for Dogs with Tumors of the Penis and Prepuce

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not improve rapidly. Administer all medications as directed. Alert your veterinarian if you are experiencing problems treating your pet.

Almost all dogs that have had surgery on their prepuce or penis will want to lick the area. This should be prevented, as excessive licking will slow the healing process and may also lead to the premature removal of sutures. Incisions that become red, swollen or have a significant discharge may be infected. Your veterinarian should determine whether antibiotics are indicated.

Animals receiving chemotherapy will need to have periodic blood tests. The CBC should be checked for any decreases in the white blood cell count. The chemotherapy may need to be adjusted based on these results.