Mass Removal?

1 / Has the cancer already spread?

To find out if a cancer has spread (“metastasized”) we do extra tests that depend on the tumor type, because different cancers spread in different ways. For example, soft tissue sarcomas often spread to the lungs, and skin mast cell tumor's usually spread to nearby lymph nodes first, then to the liver and spleen.

If the cancer has already spread, potentially aggressive treatments meant to cure will not be helpful or necessary. In those cases, we usually recommend palliative care to manage symptoms and keep the pet comfortable.

Soft Tissue Sarcomas (STS)

Three-view X-rays - right side, left side, and a top-down - are the first diagnostic test we will perform as the lungs are the most common site of spread for STS. Three views let each lung be fully inflated once and confirm that small spots aren’t hidden behind the heart or ribs.

A chest CT can reliably detect smaller spots in the lungs (≥ 1 mm) than X-rays (≥ 7 mm). CT is more expensive, so it’s usually used for tumors with a higher risk of lung spread, or when a CT is already being done for another area.

Mast Cell Tumors (MCT)

Mast cell tumor's usually spread to nearby lymph nodes first, then to the liver and spleen. There are two options to check for spread:

1. Do an abdominal ultrasound before surgery

An ultrasound looks at the spleen and liver to make sure it hasn’t already spread there before we proceed. If something looks suspicious, we can take a small needle sample (fine-needle aspiration) to confirm.

This option matters most if the mast cell tumor is high-grade (looks very abnormal under the microscope and is more likely to spread or come back), if cancer has already reached a nearby lymph node (meaning it has started to spread beyond the original lump), or when there are other worrying signs such as lethargy, loss of appetite, vomiting, diarrhea, and weight loss. The tricky part is that we usually confirm both the tumor’s grade and whether the lymph node contains tumor cells only after surgery, when a pathologist examines the removed tissues.

2. Check the lymph node at the time of surgery

Feeling a lymph node’s size isn’t a reliable way to tell if cancer has spread and needle tests often don’t give a clear answer. In one study, about 68% of samples weren’t good enough to be read, and even when they are, past research shows they miss 25-33% of cancer spread.

For this reason, we remove the nearby draining lymph node during surgery and send it to the lab for histopathology - a detailed exam under the microscope - along with the primary tumor.

Unfortunately, the “closest” (regional) node isn’t always the first-draining (sentinel) node, so removing only that node can miss spread.

Think of the body’s lymph system like a series of drain pipes and filter stations. A sentinel lymph node is the first filter that lymph fluid from a tumor passes through. It isn’t always the closest node you can feel; the “first filter” depends on how the body’s drains are routed, not the location. In dogs with skin MCT, studies show the sentinel node differs from the expected regional node in about 27%–63% of cases.

We can identify the sentinel node by injecting a tiny amount of dye near the tumor before the surgery and see which node lights up first.

2 / Do we need a biopsy before surgery?

We usually recommend biopsy before surgery when:

Large masses on the proximal limb, shoulder or hip that are likely to need a flap or graft to close after a wide excision.
Masses on the lower limb (below the elbow or knee) where skin is tight and wide margins are often not possible.

For masses on the neck or trunk, and for smaller masses on the proximal limb, shoulder or hip, we can often proceed straight to a wide excision without needing special reconstructive techniques to close the area

The key thing a pre-operative biopsy tells us is how aggressive the tumor is—its grade. Grade is one of the most important factors in predicting recurrence and therefore in deciding how much tissue to remove. If we know a tumor is low-grade ahead of time, a smaller surgery (marginal or planned narrow excision) may be appropriate. This usually makes primary closure easier and reduces wound-healing risk, while accepting the risk of the tumor coming back. The trade-off is two visits (biopsy, then surgery) and a short wait for results before moving forward.

It’s important to understand that because a biopsy looks at only a small piece of the tumor—and different parts of the same tumor can behave differently—we don’t always get the grade exactly right.

Soft Tissue Sarcomas (STS)

For soft tissue sarcomas, a biopsy is helpful but not perfect. In about 6 out of 10 dogs the biopsy grade matches the whole tumor. In about 3 out of 10 dogs, the biopsy makes the tumor look less aggressive than it really is. In about 1 out of 10 dogs, it makes the tumor look more aggressive than it really is.

In that regard, a STS biopsy is like taking one chocolate out of a box. That piece might be soft caramel, but the box could also have some pieces with nuts inside.

Mast Cell Tumor (MCT)

For mast cell tumors, a small biopsy almost always gives the right grade. It's like watching a movie trailer. Most of the time, the trailer shows you exactly what the movie will be like, but sometimes misses the “big scenes.”

In about 9 out of 10 dogs the biopsy grade matches the whole tumor. When it’s wrong, the biopsy nearly always makes the tumor look less aggressive than it really is. It never makes it look worse than it is. So if we see ‘low grade’ on a biopsy, we keep in mind there’s a small chance it could actually be more aggressive once the whole tumor is checked.

3 / Should we do a small or wide removal?

A commonly used analogy is that a tumor is like an octopus; the head of the octopus is what you can see and palpate, but the arms are extending out from the body of the octopus and these are invisible to the naked eye

There are three basic surgical approaches for tumor resection: marginal, planned narrow, and wide excision.

Marginal excision

Marginal resection is resection of the head of the octopus (what you can see and feel), knowing that you may leave the arms (microscopic disease) behind. The advantage of marginal surgical resection is that the wound following resection is more likely to be able to be closed primarily (skin edges stitched together) with a low risk of wound healing complications (< 5%); however, the disadvantage is that there is a significantly increased risk of incomplete excision and local tumor recurrence (in the case of soft tissue sarcomas, the risk of incomplete excision is 40% with marginal surgical resection) because the arms of the octopus have not been resected.

Despite this higher risk, the rates of local tumor recurrence following incomplete excision are relatively low and are dependent on histologic grade with a 7% local recurrence rate following incomplete excision of grade I STSs (≤ 1 mm of normal tissue beyond the tumor) and a 34% local recurrence rate following incomplete excision of grade II STSs.

Planned Narrow Excision

Planned narrow excision is resection of as much normal tissue (arms) as possible with the tumor while still allowing primary closure: ≤ 10 mm lateral margins plus a deep fascial plane. Using the residual-tumour (R) scheme (“tumor cells on the edges of the surgical resection” = R1), incomplete margins occurred in 42 % of STS overall. For MCT, widening the lateral cut from 0-5 mm to 6–10 mm dropped the risk of incomplete excision from 55% to just 7%. In the paper that reported these percentages wound complications were minor (26%) and none required revision surgery.

Wide Excision

With a wide surgical resection, a certain width of normal tissue is resected with the tumor to account for the entire length of the arms of the octopus.

The advantage of wide surgical resection is that there is a significantly decreased risk of incomplete histologic excision and local tumor recurrence, but the disadvantage is that there is a significantly longer duration of postoperative wound healing and a higher rate of postoperative wound healing complications. While the majority of wounds following wide surgical resection can be closed primarily, occasionally they cannot. If the wound cannot be closed, then the wound can be managed with second intention healing (it is left open and allowed to heal on its own; see image series below), flaps, or free-meshed skin grafts.

Second-intention wounds typically need protective bandages with regular bandage changes (often every 2–3 days at first) for several weeks, and even flaps usually require short-term at-home care and recheck visits. While these reconstructive techniques are usually successful in the long-term, they are more expensive and are associated with higher postoperative complication rates.

4 / What does the recovery look like?

Recovery time depends on how the wound is closed. If we can stitch/staple the skin edges together (primary closure), healing is usually fastest. If we need a skin flap, which is also a type of primary closure, healing takes longer because we move skin and its blood supply, and the flap needs time to re-establish circulation and settle without swelling or tension. If we leave the wound open to heal on its own (second intention), it takes the longest and needs more bandage care. We also adjust timelines and expectations by species - cats generally heal more slowly than dogs, so they often need longer care and more rechecks.

Primary closure (stitches or staples)

Primary closure means we bring the skin edges together right away and hold them with stitches, staples, or surgical glue. Because the skin edges touch, the body has less work to do: it seals the line, grows new skin across it, and builds strength underneath.

External skin suture removal timing:

Dogs: remove at 10–14 days if the incision is dry, non-painful, and skin edges are together.
Cats: remove at 21 days (3 weeks) under the same healing criteria.

At one week after surgery, cat skin is only about half as strong as dog skin, they can often look healed on the surface but the deeper layer isn't strong yet (false healing). That’s why we keep stitches in longer

If you see redness, discharge, gaps, or pain, keep the cone on and contact us, we may delay removal.

Second Intention Healing (left open to heal)

Second-intention healing means we do not close the skin right away. Instead, the wound heals from the inside out. Your pet’s body first grows a healthy, red “granulation tissue” bed that brings blood and healing cells. Next, the wound contracts as the edges are pulled inward. Finally, new skin (epithelium) slowly creeps over the surface.

In a study of dogs who had wide excision of masses on the lower limb (below the elbow or knee) that were left open to heal (second-intention) the typical case took about

7–8 weeks (median 53 days) to completely heal.
By 6 weeks, about 1 in 5 dogs (19%) were fully healed; by 8 weeks, about 6 in 10 (58%); by 12 weeks, about 3 in 4 (77%).

Interestingly bigger wounds did not necessarily take longer, wound size (adjusted for the dog’s body size) did not predict how long healing took.

Bandaging protects the open wound, keeps it clean and slightly moist to speed healing, and prevents licking or bumping that could reopen it. Bandages are changed every 2–3 days at first (until healthy red tissue formed; second image in the series below), then every 5–7 days until the wound fully closed. The number of bandage changes was around 13 visits for a typical 7–8-week heal (the study didn’t list a min–max number) but actual visits will vary with how quickly the wound progresses.

In cats, the same steps happen, but they form granulation tissue and regrow skin across the surface more slowly in the first 2–3 weeks. It takes cats nearly twice as long to fill a wound with granulation tissue (19 days vs 5.5 days), and they rely more on the wound edges tightening inward rather than the center pulling the wound closed as in dogs, so early progress often looks slower and total healing can take longer.

Because cat skin is looser, more pliable, and more mobile; and because cats have shorter limbs relative to a longer trunk, skin flaps are an option in more cases than in dogs

Axial pattern skin flaps (skin moved with its own blood supply)

An axial pattern flap is a piece of skin that we lift and rotate to cover a wound while keeping its own artery and vein attached. Think of it as moving skin from a nearby area like a hinged patch that brings its blood supply with it. Because the flap carries its own blood supply, it is generally more reliable than random skin flaps and can cover larger defects. Like relocating a healthy lawn patch to a problem spot while keeping the underground irrigation system “umbilical” connected.

Axial-pattern flaps usually do very well—on average, about 95% of the flap area survives. The most common problem is when the far end of the flap loses blood flow (ischemia) and the skin dies (necrosis). This can be partial-thickness (just the surface) or full-thickness (all layers of skin). We watch for hair regrowth and how the scab looks and feels to predict healing and decide if more treatment is needed.

Partial-Thickness Necrosis (surface only)

TL;DR: Soft scab + pink edges + tiny hairs = shallow problem, heals on its own.

Days 3–5: The area looks dry, dark, or scabby but still feels soft/supple, not hard or leathery.
Days 7–14: Tiny hair stubble starts poking through the scab—proof the deeper hair follicles survived.

The scab slowly lifts from the edges while healthy pink skin grows underneath. This usually heals like a scraped knee: no stitches are needed, there’s little to no scarring, and the hair coat fills in normally.

Full-Thickness Necrosis (all skin layers)

TL;DR: Hard, cold, black patch + no hair = deeper tissue loss; plan for a trim-and-clean visit.

The patch turns cold, gray-purple or black, and feels firm or leathery.
Days 5–10: A clear border/line forms between live and dead skin.

No hair grows through the dead area because the follicles are gone, and the dead piece may lift or fall off (“slough”). Once that line is clear, we remove the dead skin to prevent infection and help healthy tissue take over. After trimming, small gaps can usually heal on their own with bandage changes, medium gaps can often be closed with stitches, and large gaps may need another local flap or a skin graft to cover the area.

After removal, treatment depends on the gap size:

Small gaps: Heal on their own (second intention) with regular bandage changes.

Medium gaps: Can often be closed with stitches (primary closure).

Large gaps: May need another local flap or a skin graft to cover the area.

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