Squamous cell carcinoma (SCC) in cats is a cancer of keratinocytes, the cells that build the tough outer layer of skin, and it appears on sun-exposed, unpigmented skin. Three sites are the classic ones: the nose leather and nasal bridge, the ear tips, and the eyelid margins. The exam that settles the diagnosis is short and cheap to start: look, palpate the draining lymph node, take a cytology sample, then a 4-6 mm punch or wedge biopsy for histopathology. Everything after that is staging.
What the tumour actually is
Keratinocytes normally flatten and harden as they rise to the surface. Ultraviolet light damages their DNA, and a clone that ignores the stop signals keeps building keratin. The early stage is actinic keratosis: a rough, sandpaper patch 2-5 mm wide that never quite heals. Once the clone breaks through the basement membrane it becomes invasive SCC, and it can then reach the cartilage of the pinna or the nasal turbinates. A cat does not need a blistering sunburn for this; 30-60 minutes of daily exposure over 3-5 years is the pattern vets usually hear.
Site 1: the nose leather and bridge
Lesions start on the planum naseum or the haired bridge 5-10 mm above it, where pigment is thinnest. Early signs are a dry crack that does not respond to 2 weeks of ointment, a 1-3 mm ulcer that scabs and re-opens, or a pink raised area with a rolled edge 1-2 mm high. Cats rub the nose after eating and leave a small blood spot on the bowl rim, which owners often report before they notice the lesion. Because the nose is cartilage and thin skin, a tumour here reaches deep structures early, so the biopsy should be taken from the edge, not the crusted centre.
Site 2: the ear tips
The pinna margin is 1-2 mm thick over cartilage with almost no fat, and white ear tips take the full dose all day. Expect a crust that fails to heal in 14 days, a notch or wedge-shaped defect from self-trauma, or a raised 2-6 mm nodule on the tip. Cats with SCC of the pinna often shake the head 3-5 times a day and scratch the ear 10 or more times an hour. Look at the tip from behind, with a light behind the ear: thinning shows as a translucent window 3-5 mm across.
Site 3: the eyelid margins
A tumour within 2 mm of the lid edge produces epiphora, squinting, and a red rim that looks like chronic conjunctivitis. A 1-2 mm ulcerated nodule on the lower lid is the usual shape. Any lid lesion that persists 3 weeks despite drops needs a biopsy, and any excision within 3 mm of the margin is a specialist job, because removing too much lid leaves the eye unable to close.
The three sites side by side
| Site | Typical width (mm) | Typical height (mm) | First test | Result back (days) |
|---|---|---|---|---|
| Nose leather / bridge | 2-5 | 1-2 | punch biopsy 4 mm | 3-10 |
| Ear tip margin | 2-6 | 1-3 | wedge biopsy 5 mm | 3-10 |
| Eyelid margin | 1-4 | 1-2 | incisional biopsy 3 mm | 4-14 |
| Lip margin (less typical) | 3-8 | 2-4 | punch biopsy 6 mm | 3-10 |
The width numbers matter because they set the sampling tool. A flat 2-3 mm patch takes a 4 mm punch; a nodule over 5 mm needs a 6 mm punch or a wedge so the pathologist can see the deep border.
The examination, step by step
Step 1, history: ask how many weeks the lesion has been present and whether it has changed size in the last 30 days. Step 2, look with a bright light and a magnifier at 10x; measure the longest axis in millimetres and photograph it with a ruler. Step 3, palpate the mandibular and parotid lymph nodes and record the size in millimetres; a node over 10 mm in a cat is worth aspirating. Step 4, cytology: a fine-needle aspirate is quick and often shows keratinised cells, though heavily crusted lesions can come back non-diagnostic. Step 5, biopsy: punch or wedge, in a 2-4 mm sample, with the histopathology request marked to include margin assessment.
Blood work before any sedation means a CBC, chemistry panel, and urinalysis, usually 1 visit and 24-48 hours of waiting. If the cat is 10 years or older, add blood pressure and a thyroid check, because comorbidities are common at that age and change the anaesthetic plan.
Reading the histopathology report
Four lines carry the decision. The diagnosis line names the tumour type. The grade line calls it well, moderately, or poorly differentiated, which describes how much the cells still look like skin. The margin line gives distances in millimetres; most labs call an excision complete when tumour cells sit 2-3 mm or more from the ink. The invasion line says whether tumour has crossed into cartilage, bone, or lymphatics.
A report that says complete excision with 3 mm margins changes the plan to re-check every 3 months for 2 years. A report that says narrow or incomplete margins means a second surgery or radiation consult, usually within 2-4 weeks, before scar tissue makes the field harder to read.
What staging adds, and what it costs
Staging looks for spread, not for the primary lesion. The standard set is 3-view thoracic radiographs, an aspirate of the draining node, an abdominal ultrasound if the chemistry panel is abnormal, and a CT scan when the surgeon needs to plan margins around the nose or the orbit. Expect cytology at $60-$150, biopsy with histopathology at $250-$600, 3-view radiographs at $150-$300, and CT at $800-$1,500. The /tools/cost/ page lists how these stack up against a full workup.
Radiation is usually 15-20 fractions over 3-4 weeks and is the option when margins cannot be clean on the nose or lid. Surgery on a pinna tip can be a 20-minute procedure with 10-14 days of sutures; surgery on the nasal planum is a reconstruction and belongs with a surgical specialist.
The 14 days after a biopsy, and the years after
Keep the site dry for 10-14 days, use an Elizabethan collar if the cat can reach it, and photograph the incision on day 3, 7, and 14. Call if the wound opens more than 2 mm, bleeds for over 5 minutes, or smells. Sutures come out at 10-14 days on the pinna and 12-14 days on the nose.
Prevention is the same list for the rest of the cat's life: window film that blocks 99% of UV, no direct sun from 10 a.m. to 4 p.m. between April and September, and a full skin check every 3 months with a photo of both ear tips. A cat that has had 1 lesion is the cat to check hardest, at 6-8 week intervals in summer. Ear surgery that goes deeper than the pinna is a different problem set, covered under /health/vestibular-disease-cat/.
Terms mentioned in this article
Frequently asked
Can a vet tell SCC from sunburn just by looking?
Not reliably. Early SCC and chronic solar dermatitis look almost identical at 1-3 mm, which is why the standard move is a 4-week trial of strict shade followed by a 4-6 mm biopsy if the lesion has not shrunk by half.
How long does a biopsy result take?
Most laboratories return histopathology in 3 to 10 days, and eyelid samples can take up to 14 because they need special orientation. Ask for margin measurement in millimetres on the request form so the report answers the surgical question.
Is a needle aspirate enough to diagnose it?
Often it is not. Keratinised tumours shed few intact cells, and a crusted surface can yield only inflammatory cells. Cytology is a 60 to 150 dollar first step that sometimes confirms the diagnosis, but the biopsy remains the test that grades the tumour and measures margins.