Mammary Gland Enlargement in Cats

PetMD Editorial
May 22, 2010
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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.

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