Ovarian tumors in dogs are cancers that arise from the unregulated, disorganized development of cells within the ovary. Germ cells and epithelial (skin-like) cells are among the many cell types found in the ovary, and cancer can arise from any of them.
The majority of ovarian tumors are cancerous. Teratomas (or teratocarcinoma), carcinomas, and adenocarcinomas are some of the most prevalent malignant ovarian tumors.
The frequency of this type of cancer is quite low in North America because many dogs and cats have ovariohysterectomy (spay surgery). Malignant ovarian tumors are rare in intact (non-spayed) pets, with only 1% of dogs and even fewer cats developing them.
Cause of Ovarian Tumors
It’s difficult to say why a particular dog might acquire these or any other kinds of tumors. Only a small percentage of malignancies have a single identified etiology. The majority appear to be caused by a complicated combination of risk factors, some of which are environmental in nature and others which are genetic or hereditary. There is currently no recognized etiology for ovarian cancer. With the exception of teratomas, the majority of ovarian cancer instances occur in older, healthy canines.
Some breeds may be predisposed to the development of these tumors, including:
- German Shepherds
- Boxer Dogs
- Yorkshire Terriers
- Poodles
- Pointers
- Boston Terriers
Signs of Ovarian Cancer
The symptoms of ovarian cancer vary based on the type of tumor and where it affects the body. Ovarian tumors have a high proclivity for metastasizing (spreading), and some can produce hormones.
Many ovarian tumors are asymptomatic, meaning they show no symptoms at all. Signs may not be visible until they have grown to a large size. Fluid build-up in the abdomen, resulting in a rounded belly, is one of the clinical indicators in such circumstances.
If the tumor spreads to the lungs, fluid might accumulate in the chest, making breathing difficult. Because certain ovarian tumors produce estrogen and progesterone in excess, there may be symptoms associated with these hormones.
Vulvar enlargement, vaginal discharge, chronic estrus (menstruation and heat), pyometra (pus in the uterus), fatigue, lack of appetite, weight loss, and thinning of the haircoat are all symptoms to look out for.
How Ovarian Cancer is Diagnosed
Initially, these tumors can be difficult to detect, but they can be detected by a physical exam or normal bloodwork. Your veterinarian may palpate (feel) a significant mass in the belly, see certain external indications, such as a large vulva or vaginal discharge, and look for abnormalities in bloodwork during a physical examination.
Your veterinarian may consider an ovarian tumor if your pet has a pyometra (uterine infection) or other disorders that might arise as a result of increased and aberrant hormone production.
In some cases, elevated calcium may be observed on bloodwork which may indicate further diagnostics tests (i.e., X-rays or abdominal ultrasound), at which point the tumor may be found.
Some tumors will produce hormones that not only cause your pet’s vulva to look larger than normal but will also be apparent on bloodwork.
By far, abdominal ultrasound or a spay operation is the most prevalent ways to diagnose ovarian cancer (ovariohysterectomy). If you have a spay procedure, any abnormal tissues will be sent to a pathologist for assessment, which is known as histopathology. The pathologist can next examine the tissues under a microscope to determine the type of tumor and whether or not it is malignant.
Recommendations for Ovarian Cancer in Dogs
Ovarian tumors are generally more locally aggressive (meaning they penetrate local tissues) and have a low rate of metastasis (spread to other parts of the body). Metastasis occurs in just approximately 20% to 30% of instances.
Prior to surgery, your veterinarian may propose comprehensive staging (looking for probable metastasis to other parts of the body). Blood tests, urinalysis, X-rays of the lungs, and potentially an abdomen ultrasound are all possible tests. If any abnormalities are identified, these sites may be tested before or during surgery to see if cancer has spread to other parts of the body.
Treatment of Ovarian Cancer in Dogs
The most common and pursued therapeutic option is ovariohysterectomy (spay). It is the treatment of choice for benign or locally developing cancers because the tumors are entirely eliminated.
If staging and other diagnostic tests reveal that cancer has metastasized (spread to other parts of the body), a spay treatment with removal of other afflicted tissues or lymph nodes may still be undertaken.
Chemotherapy may be used as a followup, albeit there is limited evidence of its effectiveness.
Final Thoughts
Given that the majority of pet owners in North America sterilize their dogs, these tumors are quite rare. Breeding animals exposed to fluctuating sex hormones for an extended period of time, with recurrent estrus cycles and pregnancies, may be more prone to developing malignant tumors. However, for many of these malignancies to be treated, spaying is usually required.
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