Mammary Gland Enlargement in Cats

Mammary Gland Hyperplasia in Cats

Mammary gland hyperplasia is a benign condition in which an an excessive amount of tissue grows, resulting in enlarged masses in the mammary glands. This is primarily limited to young, sexually intact, cycling, or pregnant queens, but it can also affect cats of either gender after neutering, and cats of either gender that are on progestogen medication.

Symptoms and Types

  • Enlargement of one or more mammary glands
  • Firm, nonpainful masses in the chest, and abdominal area


  • Secondary to a progesterone influence
  • May develop after neutering; the illness may involve progesterone, growth hormone, or prolactin (a peptide hormone primarily associated with lactation)
  • High progesterone – may be associated with false pregnancy in a queen that has been induced to ovulate but has remained nonpregnant for 40–50 days after ovulation induction, or in pregnant queens throughout the gestation period
  • Associated with administration of prescription progestogen


Your veterinarian will need to differentiate between several possibilities to arrive at a reliable diagnosis. Fluid will be expressed from the mammary gland for laboratory analysis, and a biopsy of the tissue may also be analyzed to determine the exact cause of the excessive tissue growth, and whether the growth is in fact, of a benign or malignant (cancerous) nature. Mastitis (infection of the mammary glands) can usually be ruled out based on the absence of symptoms, such as painful glands and fever, but the presence or absence of bacteria in the expressed fluid will definitively rule out infection.


The process of the maturation and release of eggs

mammary glands

The glands in female animals that are used to produce milk; also called the udder or breast


A compound made up of a group of amino acids; aids in the digestion of certain proteins


A hormone that is created at the time of pregnancy


A hormone involving the secretion of milk


Something that becomes worse or life threatening as it spreads


The formation and secretion of milk and the processes involved


The process of removing tissue to examine it, usually for medical reasons.


The period that an animal is pregnant in which the fetus develops from conception to birth

growth hormone

The hormones that stimulate growth of the body


Denotes an animal that is still able to reproduce or is free of cuts and scrapes


Not being able to cause harm; the opposite of malignant.

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