CANINE MAMMARY TUMOR

This segment is intended to give an insight on canine mammary tumors its  direct correlation of the intact uterus and ovaries and the  effect of early  neutering in dogs .

In our university hospital on an average we receive 5-8 cases per week presented with advance canine mammary tumors  . It is a great concern for the dog owners as there is a large awareness among the cancer in human beings. But it is a sad reality that even the most educated pet owner is not fully aware of the direct correlation between the mammary tumor and the intact uterus and ovary in dogs . 

CANINE MAMMARY GLAND - ESSENTIAL  ANATOMY

The number of teats in the dog varies from 8 to 12, with 4 to 6 gland complexes on each side of the midline. Ten is the most common number in larger breeds, four pairs are more common in the smaller breeds. In bitches with ten normal teats, the pattern is two pairs thoracic teats, two pairs abdominal teats, and one pair of inguinal teats.

The number of ducts opening on a teat varies from 8 to 20 external openings per teat for the dog and 1 to 7 for the cat. The openings are located on the blunt end of the teat in an irregular pattern.

The parenchyma, or secretory tissue, is present only during pregnancy, pseudopregnancy, during lactation, and for 40 to 50 days after weaning.

The blood supply of the mammary glands of dogs and cats are similar except for the thoracic glands. In the dog the first pair of thoracic mammary glands receives blood from two sternal branches of the internal thoracic artery, passing between the first and second ribs. The second pair of thoracic mammary glands is supplied by small branches of the mediastinal, or internal mammary, arteries before they anastamose with the sternal branches serving the first pair of glands.

MAMMARY TUMORS

Tumors are frequently seen in the mammary gland of the dog. They may belong to the connective tissue or the epithelial series of mammary tumors, or both. Tumors of the epithelial series are of great importance. Those observed are adenomas, carcinomas, and above all, mixed mammary tumors.

The risk of breast cancer is almost eliminated in dogs that are spayed before their first heat.
Spaying greatly reduces the chances of a female dog developing this condition.

 In those females spayed prior to their first heat cycle, breast cancer is very, very rare. The risk of malignant mammary tumors in dogs spayed prior to their first heat is 0.05%. It is 8% for dog spayed after one heat, and 26% in dogs spayed after their second heat. It is believed that the elimination or reduction of certain hormonal factors causes the lowering of incidence of the disease in dogs that have been spayed. These factors would probably be estrogen, progesterone, a similar hormone or possibly a combination of two or more of these.

The development of mammary gland neoplasms appears to be hormone-dependent because the risk of developing a mammary tumor increases as the number of estrous (heat) cycles increases.

Normal mammary tissue and a majority of benign tumors express both estrogen and progesterone receptors. Less than 50% of mammary carcinomas express either of these receptors. This observation suggests that there is a loss of hormone dependency during transition to malignancy.

Common Signs

Abnormal swellings that persist or continue to grow

Sores that do not heal

Weight loss

Loss of appetite

Bleeding or discharge from any body opening

Offensive odour

Difficulty eating or swallowing

Hesitation to exercise or loss of stamina

Persistent lameness or stiffness

Difficulty breathing, urinating, or defecating

Mammary carcinomas may exhibit rapid growth, doubling in size within a few weeks. However, the size and appearance of these neoplasms can vary greatly. Inflammatory carcinomas usually have diffuse involvement of multiple mammary glands. Edema, erythema, and firmness may be present and affected mammary glands may feel warm to the touch. Dogs with inflammatory carcinoma are more likely to have generalized weakness with anorexia and weight loss. Inflammatory carcinoma is often misdiagnosed as acute mastitis.

TYPE OF TUMORS 
The following are common classes of mammary tumors that might be found on a biopsy.

Fibroadenoma:
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.

Adenocarcinoma: 
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.

Inflammatory Carcinoma:
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.
The malignant mammary tumors thus in general includes

Tubular adenocarcinomas

Papillary adenocarcinomas

Papillary cystic adenocarcinomas

Solid carcinomas

Anaplastic carcinomas

Osteosarcomas

Fibrosarcomas

Malignant mixed tumors.

Diagnosis of Mammary tumors

Mammary gland tumors are difficult to diagnose by routine cytology and the malignant potential of mammary neoplasms cannot be easily detected in early stages by cytologically.

The cytologic criteria for malignancy in Mammry tumors are

Anisocytosis (variable nuclear size)

Nuclear giant forms

Nuclear or cytoplasmic membrane distortions

High nuclear to cytoplasmic (N:C) ratio

Irregular chromatin shape

Variable chromatin size

Presence of macronucleoli

Variation in nucleolar number

Variation in nucleolar shape

Parachromtin clearing

Hormones 

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.

MANAGEMENT OF CANINE MAMMARY TUMOR 

Surgical removal of the tumor(s) is the treatment of choice for benign mammary tumors and for malignant mammary tumors that have not spread beyond the mammary tissue and adjacent lymph nodes. If  surgery is done early in the course of this disease, the cancer can be totally eliminated in over 50% of the cases having a malignant form of cancer.Most benign mammary tumors are curable by surgery. Approximately half of malignant mammary tumors are also cured by surgery. This is possible because some malignant mammary tumors in the dog do not spread very quickly and can be removed before they spread. Radical mastectomy has not been shown to be any more effective than more limited surgery. Tumors that are larger than 3 centimeters and tumors that are of higher grade (as classified by the pathologist) are more likely to recur (70% recurrence at 1 year) than smaller tumors and tumors of a lower histopathologic grade (30% recurrence at 1 year). If the dog is not spayed at a young age, spaying at the time of mass removal has recently shown to increase the survival time for some dogs with malignant tumors.

Different terminologies are related to the surgical resection of mammary gland

Mammectomy

Removal of one entire mammary gland, indicated for lesions involving 1/3 of the gland or that are fixed to skin or fascia. Remove skin, abdominal wall fascia.

Regional mastectomy

Removal of affected gland and adjacent mammary glands based on known venous/lymphatic drainage of mammary tissue (may involve axillary, superficial inguinal, sublumbar and cranial sternal nodes).

En bloc mastectomy

Resection of affected glands with the regional lymph node(s)

Unilateral or bilateral (radical) mastectomy

Indicated if multiple tumors or several large tumors along one or both mammary chains, or for any malignant mammary gland tumor in cats.

Chemotherapy: An effective chemotherapy protocol for canine mammary cancer has not been defined. A small percentage of dogs have had remission with drugs such as doxorubicin (Adriamycin) or cisplatin. Because surgery alone is successful in many cases, chemotherapy is usually reserved for tumors that cannot be removed surgically, tumors that have metastasized, and tumors that have a high probability of spreading. Radiation therapy has not been extensively studied to in dogs with mammary tumors. The chemotherapeutic protocol which  can be tried will be a combination of 5-fluorouracil (150 mg/m2 of body surface  area) and cyclophosphamide (100  mg/m2)  but the sideffects masks the results. Postoperative Adjuvant Treatment of Invasive Malignant Mammary Gland Tumors in Dogs with Doxorubicin and Docetaxel has also given excellent results for many practitioners .

A word of caution is always advisable using doxyrubicin . In one case I had encountered a very adverse reaction and tachy cardia associated with doxyrubicin.

Metastasis is a common feature of malignant mammary tumors and chest radiographs will reveal the metastatic nodules in lungs in most of the advanced carcinomas. 

Some cases give real challenges with multiple lesions 

PLEASE WATCH THE VIDEO BELOW 

PREVENTING MAMMARY TUMORS

There is a direct correlation between the early spaying of female dogs and the reduction in the incidence in mammary cancer.

Dogs spayed before coming into their first heat have an extremely small chance of ever developing mammary cancer. 

Dogs spayed after their first heat but before 2.5 years are at more risk, but less risk than that of dogs who were never spayed, or spayed later in life. As a veterinarian I strongly believe that .......MAMMARY TUMORS ARE  PREVENTABLE  BY EARLY SPAYING .