Thank you for your question regarding your 13 year old girl who has just been diagnosed with breast cancer. You must be rather worried at the moment, however do not fret as many of these are very responsive to surgery and I would definitely recommend this for your girl. Her overall prognosis really does depend upon the type of tumor she has and your Vet should have worked this out by now. Basically only 50% of canine breast tumors are malignant compared to 95% in the cat. This immediately gives your girl a great chance!
I really want you to read the following information on canine mammary tumors from a Veterinary only website. It is very informative and will help ease your mind.
If your dog is unspayed, was known to have had puppies, or was spayed in adulthood, she fits into the high-risk group for mammary cancer development. It is important to be somewhat familiar with the normal mammary anatomy of the female dog. There are ten sets of mammary glands as shown though the average female dog has only nine. (It is not unusual for asymmetry of mammary glands to be found.) The normal glands should be soft and pliant, especially towards the rear legs. There should be no firm lumps. If a lump is detected, see your veterinarian at once regarding possible removal. Most tumors occur in the glands nearest the rear legs.
Benign vs. Malignant
The good news, if there is some, is that approximately 50% of the tumors formed by female dogs are benign. Since one cannot tell which it is by looking at a tumor, the tumor or part of it must be removed and sampled for biopsy. The laboratory can determine whether the tumor is benign or malignant based on the cells and their architecture within the tissue. Alternatively, a needle aspirate can be performed, in which a syringe is used to withdraw some cells from the growth and the laboratory can determine whether the tumor is benign or malignant with enough accuracy to determine how aggressive the surgical approach should be. Needle aspirate may be a helpful pre-operative procedure in many cases, but it should be understood that biopsy is ultimately what is necessary to determine the extent of disease.
Approximately 50% of malignant mammary tumors in the dog have receptors for either estrogen or progesterone. This means that the presence of these female hormones promotes the growth of these tumors. Benign tumors also have female hormone receptors and can also be stimulated by hormonal cycling of the female dog. This means that spaying is important even if a tumor has already developed; in one study, female dogs spayed at the time of mammary tumor removal or two years prior lived 45% longer than those who remained unspayed.
Types Of Tumors
The following are common classes of mammary tumors that might be found on a biopsy.
A benign glandular tumor for which no treatment is necessary.
Mixed Mammary Tumor:
What is mixed is the type of cell that makes up the tumor: the epithelial cells that line the glandular tissue and the mesenchymal cells that make up the non-glandular portion. (Mixed does not refer to a mix of benign and malignant cells.) The mixed tumor can be either benign or malignant and the biopsy will indicate this.
Adenocarcinomas can be tubular or papillary, depending on the gland cells the tumor arises from. Adenocarcinomas behave malignantly but how aggressively malignant they are depends not on whether they are tubular or papillary, but on other cellular characteristics described by the pathologist (such as how quickly the cells appear to be dividing and how closely they resemble normal gland cells). When the oncologist reads the description he or she will be able to determine how aggressively to combat the tumor.
A highly malignant tumor that generates tremendous inflammation locally with ulceration, pus, and discomfort. This type of tumor tends to spread early in its course and is difficult to treat. Fortunately, this especially tragic tumor type accounts for less than 5% of mammary tumors.
In general: approximately 50% of malignant mammary tumors will have already spread by the time of surgery.
This, of course, means that the other 50% are locally confined and surgery is curative.
What Else Determines Prognosis?
The type of tumor is obviously important in determining the prognosis; further, spaying at the time of tumor removal or prior is also an important factor in determining prognosis. Other factors include:
- The size of the tumor. Tumors with diameters larger than 1.5 inches have a worse prognosis than smaller tumors.
- Evidence of spread to the lymphatic system (such as the presence of tumor cells in a local lymph node or visible tumor cells with in lymphatic vessels on the biopsy) carries a worse prognosis.
- Deeper tumors or tumor adherence to deeper tissue structures carries a worse prognosis.
- An ulcerated tumor surface carries a worse prognosis.
- A history of especially rapid growth carries a worse prognosis.
The biopsy sample will not only identify the tumor type, it will also indicated whether or not the tumor was completely removed (so called "clean" or "dirty" margins).
If the tumor was not completely removed, one may wish to consider a second surgery to remove more tissue.
Radiation therapy, chemotherapy, and anti-estrogen therapy have been used for incompletely removed tumors. Sometimes it is most appropriate to monitor for recurrence with periodic chest radiographs.
As you can see, it really does depend on whether this tumor is benign or malignant as to the ultimate prognosis and even if it is malignant, depending on spread, surgery is definitely indicated. You really will need to discuss this further with your Vet to understand more about your girls specific tumor and as to the chances after surgery.
Do not fret and please get in touch with your Vet again soon. I have seen many of these cases at my clinic and the majority I have personally seen have been benign cases.
Please reply if you require any further information and don't fret in the mean time.
Thank you and please now click ACCEPT!!
Dr M D Edwards