A lump on a cat belly is not the same problem as the same lump on a dog. Treat every mammary mass in a cat as potentially malignant until histology says otherwise, and do the work-up in 3 steps: cytology, staging imaging, then excision with histology and lymph node sampling. The pathology report should come back with 3 letters filled in — T, N and M — and a grade, because those 5 fields decide the next 12 months of visits.
Why position and size decide the plan
Cats have 8 mammary glands in 4 pairs, running from the armpit to the groin, and the two front pairs carry most of the tumors. A mass in the armpit is easy to mistake for a lymph node, and one in the groin for a hernia or an abscess, which is why a 1 cm lump can sit for weeks before anyone measures it. Measure with calipers in 3 dimensions in millimetres and write the number in the record. A mass that crosses 1 cm, or doubles within 4 weeks, moves from watch to work-up.
Check 1: fine-needle aspirate
A 25 to 27 gauge needle, 3 to 5 passes, no sedation in most cats, results in 1 to 2 days and 50 to 150 dollars. Cytology separates inflammation, cyst fluid and round-cell tumors from epithelial masses, and it tells you whether the chest wall or skin is involved before anyone books surgery.
Its limit matters more than its result: cytology cannot reliably separate a benign adenoma from a carcinoma in a cat, and a sample of 20 to 30 cells can miss a malignant clone sitting 2 mm away. A report that reads benign does not cancel surgery on a 2 cm mass that is still growing.
Check 2: staging imaging
Three-view chest radiographs — right lateral, left lateral and a ventrodorsal view — plus abdominal ultrasound. The extra lateral view matters: nodules behind the heart or under the diaphragm hide on a single film, and CT finds 3 to 5 mm nodules that plain film misses entirely. Ultrasound covers the liver, the medial iliac and inguinal lymph nodes and both adrenal glands, and it takes 20 to 30 minutes.
Add a blood panel and urinalysis for anaesthetic safety, and ask for a clotting check if the mass is ulcerated. Book imaging within 7 to 14 days of the aspirate, and always before surgery, because a lung nodule changes the plan from cure to control.
Check 3: histology and the node
Excision with 2 cm margins where the anatomy allows, plus sampling of the draining node — axillary for the front pairs, inguinal for the back pairs. Histology reports in 5 to 10 business days and should state tumour type, grade I to III, mitotic count per 10 high-power fields, lymphatic or vascular invasion, and the closest margin in millimetres. A margin of 5 mm or more reads differently from a margin of 1 mm, and the number belongs in your own file, not just the clinic computer.
Reading T, N and M
| Field | Code | Definition | Typical size |
|---|---|---|---|
| Tumour | T1 | Confined to the gland | under 1 cm |
| Tumour | T2 | Confined, larger | 1 to 3 cm |
| Tumour | T3 | Confined, large | over 3 cm |
| Tumour | T4 | Skin or chest wall invaded | any size |
| Node | N0 | No spread found | under 5 mm |
| Node | N1 | Movable node involved | 5 to 20 mm |
| Node | N2 | Fixed node involved | over 20 mm |
| Metastasis | M0 | No distant spread | 0 sites |
| Metastasis | M1 | Distant spread found | 1 or more sites |
Stage then follows in 4 steps: stage I is T1 N0 M0, stage II is T2 N0 M0 or T1 N1 M0, stage III is T3 with N0 or N1, and stage IV is any T with M1 or a T4 tumour. Cut-offs vary by a few millimetres between staging systems, so ask which one your lab used and keep the same one at every recheck.
Timeline and what it costs
| Step | Day | Cost range | Result wait |
|---|---|---|---|
| Exam, aspirate | 0 to 2 | 50 to 150 | 1 to 2 days |
| Chest films, 3 views | 3 to 7 | 150 to 300 | same day |
| Abdominal ultrasound | 3 to 7 | 250 to 450 | same day |
| Blood panel, urine | 3 to 7 | 80 to 200 | 1 to 2 days |
| Mastectomy, one chain | 10 to 21 | 800 to 2,000 | 5 to 10 days |
Two chains removed at once costs more and adds 30 to 60 minutes of anaesthesia; many surgeons stage the two sides 3 to 4 weeks apart when both need removal. The cost planner is the place to add these lines up before the consult rather than after.
The 8 glands and the surgery decision
Removing one chain takes 4 glands and 45 to 90 minutes; a bilateral case is either one long procedure or 2 operations 3 to 4 weeks apart. A drain stays 3 to 5 days, a soft cone stays 10 to 14 days, and skin sutures come out at day 10 to 14. Spaying at the same time is common and adds 10 to 20 minutes; spaying before the first heat is the version that lowers risk in the first place.
Rechecks after the report
Book the first recheck at 14 days for the wound, then every 3 months for the first 2 years with chest imaging every 6 months, then every 6 months. Weigh the cat at every visit and measure the scar with calipers; a 3 mm nodule at the scar edge at month 4 is a finding, not a wait-and-see. Keep the histology report number in your phone.
When to go sooner
Ulceration, a mass fixed to the abdominal wall, a cat that stops eating for 24 hours, or a lump that grows 5 mm in 2 weeks all shorten the timeline. A sudden head tilt in an older cat is usually not spread; the pattern of that sign is set out in vestibular disease in cats, and a mouth mass is a separate work-up covered in oral tumor signs.
Five steps after you find the lump
- Measure it in 3 dimensions in millimetres and photograph it next to a ruler today.
- Book an aspirate within 7 days; ask for the cytology report in writing.
- Do 3-view chest films and an abdominal ultrasound before any surgery date.
- Ask the surgeon to sample the draining node and to state margins in millimetres.
- Put the T, N, M and grade on the fridge, and book the 3-month recheck before you leave.
Terms mentioned in this article
Frequently asked
The aspirate came back benign. Can I skip surgery?
Usually no, if the mass is over 1 cm or still growing. In cats, cytology of a mammary lump cannot reliably separate an adenoma from a carcinoma, and a 20 to 30 cell sample can miss a malignant clone a few millimetres away. Ask for the actual description, not just the conclusion, and ask what the plan is if the mass doubles over the next 4 weeks.
Why does the report need T, N and M instead of just a diagnosis?
Because the 3 fields answer 3 different questions. T is how far the primary tumour has grown and whether it has reached skin or chest wall, N is whether the draining node is involved and whether it can still move, and M is whether anything has spread beyond the region. Those answers set the recheck interval, the imaging schedule and whether a second surgery is worth planning.
How soon should surgery happen after the lump is found?
Most surgeons want the staging images and bloodwork back within 7 to 14 days of the first visit, and the operation within 2 to 3 weeks of that, so a 10 to 21 day window from the aspirate is common. Waiting longer is reasonable only when the mass is small, stable and measured at every visit with the same calipers.