Adenocarcinoma means cancer arising from glandular epithelial cells. Growth rate and detected spread vary, and not every cat has metastases at diagnosis. A small or painless lump still needs investigation because appearance cannot reliably identify its nature.
When to see a vet urgently
Seek emergency care if your cat has any of the following:
- Laboured or open-mouth breathing at rest.
- Collapse or unusual unresponsiveness.
- Heavy or persistent bleeding from an ulcerated lesion.
- Severe pain and markedly poor general condition.
Otherwise, arrange prompt examination of a new mammary lump. You can find a vet near you. Do not remain at home investigating breathing difficulty.
Overview
Mammary tumours are fairly common in cats, and around 80–90% prove malignant. Adenocarcinoma grows quickly, ulcerates easily and metastasises early. Tumours are most often found in unspayed cats over eight years old. Spaying before the first season sharply reduces malignant tumour risk.
Adenocarcinoma is a malignant diagnosis, whereas a mammary lump may prove to be another change. Inflammation and benign hyperplasia, for example, are differential diagnoses. The high proportion of malignant mammary tumours warrants prompt investigation, but is not a laboratory result for an individual lump.
Several lumps may be present simultaneously, so the vet examines every mammary gland. Previously spayed cats can also develop the disease. Early spaying reduces risk but does not remove the need to investigate a new lump.
Causes
The main factors associated with mammary adenocarcinoma include:
- Hormonal effects: prolonged oestrogen and progesterone exposure in unspayed females.
- Remaining unspayed or being spayed late.
- An inherited predisposition.
- Age, with greater frequency in older cats.
Evidence for heredity in cats is weaker than for hormonal exposure. An observed breed-related risk does not establish an inherited cause in an individual cat either. Tumour development is not usually explained by one factor.
Risk factors
- Unspayed females over six to eight years old.
- Use of hormonal medicines to suppress seasons, sometimes called contraceptive pills.
- Breed predisposition, with greater frequency in Siamese cats.
- Chronic mammary inflammation or injuries.
Chronic inflammation or injury alone is not used to measure cancer risk, because feline evidence for these as independent adenocarcinoma risk factors is limited. Do not explain a new lump as an old knock without investigation. The age threshold does not rule out disease in a younger cat either.
Typical symptoms
- Lumps and firm areas around mammary glands.
- Tenderness and redness over the tumour.
- Ulceration and discharge.
- Enlarged nearby lymph nodes.
- Weight loss and reduced appetite.
- Coughing and breathlessness when lung metastases are present.
An early lump may be small, mobile and painless, without red skin. Do not wait for ulceration, weight loss or deterioration before booking. Report when it was found and whether it has grown or begun discharging.
The absence of coughing or breathing difficulty does not exclude lung metastases. A cat may look normal even with advanced disease. Conversely, not every respiratory sign is caused by cancer; investigations assess the cause rather than the cancer diagnosis alone.
Complications and consequences
Mammary adenocarcinoma is extremely dangerous for cats:
- Rapid local tumour spread.
- Metastases to lymph nodes and lungs.
- Tumour ulceration and infection.
- Wasting and death without treatment.
Diagnosis at the vet
- Clinical examination and mammary palpation.
- A cell or tissue sample to confirm diagnosis.
- X-rays and ultrasound of the chest and abdomen to look for metastases.
- Complete blood count and biochemistry to assess general condition.
What do samples show?
Fine needle aspiration collects cells and may help identify the lesion initially. Histology, microscopic tissue examination, provides a more precise diagnosis and information about tumour grade. Grade describes how abnormal the cells look and the aggressive behaviour predicted by the finding.
Removed tissue can also be assessed for invasion of blood or lymphatic vessels. This information affects further treatment decisions. Knowing only that a lump has been removed does not establish the full disease extent or recurrence risk.
Assessing spread
Staging investigations are performed before treatment decisions where possible. Chest imaging looks for lung changes, while abdominal examination assesses other possible spread or concurrent illness. The imaging method is selected according to the question and patient.
Nearby lymph nodes may be sampled even when they feel normal-sized. Normal size does not reliably exclude tumour cells. Conversely, enlargement alone does not prove metastasis, so cytology or histology helps interpret the finding.
Routine blood tests help assess organ function and treatment tolerability, among other factors, but normal blood values do not exclude cancer. Report every illness and medicine so anaesthesia and further treatment can be tailored appropriately.
Treatment
- Surgery is the main treatment: the entire mammary chain on the tumour's side is removed, often both chains in two stages, reducing recurrence risk.
- Tumour size matters: the prognosis is considerably better for tumours under 2 cm than those at least 3 cm. Seek veterinary care promptly for any firm area on the abdomen.
- The vet may suggest chemotherapy after surgery.
Surgical extent and staging depend on lump location, number, findings and general condition. The goal is the best possible local control. Removed tissue is examined to provide a more precise basis for further care.
Removing a local tumour and controlling cells elsewhere in the body are different goals. Chemotherapy may be considered for high spread risk or confirmed metastases, for example. However, studies have not consistently demonstrated additional benefit after surgery, so goals, uncertainty and possible adverse effects are discussed with you.
Widespread disease or unsuitability for major surgery may shift the emphasis to symptom relief. Palliative care means relieving pain and other symptoms and supporting function. It can also accompany other cancer treatment and need not be postponed until the final stage.
Home care after surgery
Discharge instructions cover pain relief, wound protection and activity restrictions. Prevent licking and scratching using the supplied protection. Make resting places, food and the litter tray easy to reach so your cat need not strain or jump and pull on the wound.
Check the wound as directed. Report increasing swelling, redness, discharge, bleeding or separation of wound edges. Do not apply your own creams or disinfectants without instructions. Hiding, avoiding touch and reduced movement may also indicate pain.
Monitor actual food intake and weight trends. If your cat will not eat, ask for help planning nutrition; force-feeding is not a universally safe solution. Report nausea, vomiting and difficulties giving medicine too. The goal is pain relief and feeding that work in practice.
Monitoring and prognosis
A small tumour without detected spread generally provides a better starting point than a large or metastatic tumour. Size alone does not determine lifespan, however. Lymph nodes, metastases, tumour grade and delivery of treatment also affect the prognosis. Average study survival times are not deadlines for an individual cat.
Check-ups assess the surgical area, other mammary glands and lymph nodes, with repeat imaging when needed. Even a symptom-free cat may need monitoring. Report a new lump, wound change or altered breathing before the next scheduled visit.
At home, assess eating, movement, rest and interest in familiar activities. The plan may change if adverse effects increase or benefit is limited. Quality of life support remains part of care even when the tumour cannot be removed completely.
Prevention
- Spaying before the first season is the most effective prevention. Studies suggest spaying before six months reduces risk by around 90%, and before one year by around 85%.
- Do not use hormonal medicines to control seasons.
- Regularly feel an unspayed female's mammary glands, particularly after six years of age.
- Seek veterinary care promptly for firm areas.
Early spaying reduces risk, but the percentages describe relative risk reductions in study groups rather than complete protection. Mammary changes therefore need checking after spaying too. Discuss hormonal medicine use with the vet, and do not manage an established tumour with preventive spaying alone.
Important for cat owners
Mammary adenocarcinoma is one of the most aggressive cancers. Remember that earlier detection and surgical removal, often of the whole mammary chain, offer better chances of extending life. Preventive spaying is the most reliable protection. Even the smallest firm area warrants a veterinary visit without delay.
This article provides general information and does not replace veterinary care. Contact a vet if you notice signs of illness in your cat.
Frequently asked questions
Can a small, painless lump be cancer?
Yes. An early tumour may be painless with intact skin while the cat remains well. A new mammary lump needs examination without delay.
Do normal lymph nodes exclude metastases?
No. Tumour cells may occur in normal-sized nodes. Sampling and other staging investigations complement palpation.
Does every cat need chemotherapy?
The decision is individual, based on spread, histology and wider health. Research does not show an unambiguous additional benefit from postoperative treatment.
Can a spayed cat develop mammary cancer?
Yes. Early spaying substantially reduces risk but does not eliminate it. A new lump in a spayed cat also needs investigation.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
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- 2023 AAFP/IAAHPC Feline Hospice and Palliative Care Guidelines, American Association of Feline Practitioners and IAAHPC, accessed 2026-11-05.
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