Mammary gland tumor:

• A mammary tumor is a new plasma originated in mammary gland
• It is a common finding in older female dogs and cats that are not spayed but they are found in other animals as well .

Etiology:

• Dogs are susceptible to a wild variety of mammary gland neoplasm, most of which are influenced by circulating reproductive steroidal hormone
• example:

Progesterone increases the risk for developing mammary cancers in dog

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Progesterone stimulate growth factor (molecules that stimulate specific processes in body)

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That causes mammary cells to multiply

Clinical signs:

• Single nodules are found in approximately 75% of cases of canine mammary tumors
• Nodules or palpable masses can be found in glandular tissue or associated with the nipple
• Masses in two caudal glands (4th and 5th) account for a majority of tumors
• Benign tumors tends to be small , well circumscribed and firm, whereas malignant tumor are larger and invasive and coalesce with adjacent tissue
• Occasionally, the skin over masses may ulcerate and bleed and effected area may feel warm to touch and become painful
• Mammary gland may even develop a discharge

Pathogenesis:

• Mammary tumor of dog develop under the influence of hormone
• Receptors for both estrogen and progesterone can be found in 60-70% of tumors
• The risk of developing mammary tumor increased greatly after 1ST and 2nd estrus cycle
• Dogs spayed prior to first estrus have risk 0.8% and after 1st and 2nd estrus risk will be 8% and 26% respectively.

• Malignant mammary tumors typically spread through the lymphatic vessels.
• Metastasis from 1st, 2nd and 3rd mammary glands is to the ipsilateral axillary or anterior sternal LN.
• 4th and 5th mammary glands drain to superficial inguinal LN where metastasis can be found.
• Many mammary carcinomas will eventually metastasize to lungs

• In dogs, mammary tumor are 2nd most common tumors (after skin tumor)
• And most common in females.
• 3rd most common in cats following lymphoid and skin cancer.

Classification of mammary carcinomas depending on biological behavior ,

• Taking into consideration the histological aspects
• Stage 0:

Malignant proliferation is limited to the anatomical structure of mammary ducts,             carcinomas in situ

• Stage 1:

  malignant proliferation extend beyond anatomical limits of mammary duct, invading adjacent stroma, invasive carcinoma, with vascular and lymph node identification

• Stage 2: carcinoma with vascular or lymphatic invasion or metastasis in regional lymph node
• Stage 3: obvious metastatic disease

Pathological findings

• Based on histological classification of mammary gland tumor:
• Approximately half are benign(fibroadenomas, simple adenomas and benign mesenchymal tumor)
• Half are malignant(solid carcinomas, tubular adenocarcinomas, papillary adenocarcinomas, anaplastic carcinomas, sarcomas and carcinosarcomas)