The removal of tumors of all types and sizes is a broad topic:
Many of the masses that we vets remove are easy to see or feel on the surface of the body and are usually easy to remove.
But other mass removal surgeries are a major undertaking:
Some masses and cancers have a huge blood supply.
Some masses and tumors are easy to identify and separate from surrounding tissues and easy to tease out of the body, but sometimes it's very hard to tell what's cancer and what's normal tissue.
Some masses are fairly easy to peel off the surface of whatever organ they are attached to, but sometimes the tumor infiltrates the organ and the surgeon has to decide how much to cut out. After all, many organs are too vital to remove.
There's another problem:
Patients with masses tend to be older, and older patients are more likely to have additional problems, are less quick to heal, tend to have weak cardiovascular systems, and tend to be either over-weight or emaciated by their disease.
Pre-anesthetic testing for these patients, careful anesthetic choices and monitoring are more critical than in young patients.
Patients with cancer are more likely to be immune suppressed.
Another part of the equation: are we risking surgery for nothing if the cancer has spread to other parts of the body? To help rule out this possibility, your vet may want to biopsy area lymph nodes, get radiographs or ultra sound images.
Or send you to a veterinary specialty center for possible MRI or CAT Scan images.
And of course, your vet may recommend that you go to a specialist for a second opinion and for the surgery; it's a rare general practioner who routinely does tumor removal from the chest, spine, or brain.
More things to consider:
Sometimes the recovery is more involved than the actual surgery what with daily management of wound drains, post op nausea, and so forth.
Then there's the question of whether or not we were successful in removing all the cancer. Usually there are microscopic remains of the cancer a little distance from the visible tumor. To be certain, biopsies of the surrounding tissue need to be sent off to the pathology lab.
Sometimes multiple surgeries are needed.
Another big complication involves bleeding. Some tumors are highly vascular and a lot of time is needed to get bleeding under control. In such cases, recovery is complicated from blood loss and long anesthetic time.
Mammary tumors are often very vascular as well as spread out.
Some cancers seem to like to grow in some pretty inconvenient places. It's no big deal to peel a little mass out from under the skin, but sometimes the masses go deep into the nose, jaw, eye, ear canals, throat, anus, eyelids, and genitals.
And finally, it's becoming more and more common to combine surgical reduction of cancers with chemotherapy and/or radiation therapy.
The success rate for treating various types of cancer has improved by leaps and bounds in recent years. Don't be too quick to give up on your pet friend just because the diagnosis is cancer.
There's lot more general information about cancer in cats and dogs on our cancer page.
As for what to expect in terms of the surgery itself, please read the general considerations involved in any surgery on our introductory page about surgery if you haven't already. Whether or not the surgery is relatively routine and minor or a major undertaking will depend on where and what type of cancer is causing the problem.
Whether or not you have your local vet simply remove the obvious mass to make your pet more comfortable or you have your pet referred to specialists expert in cancer (Oncology) surgery, chemotherapy, and radiation therapy will depend on how aggressive you're willing to be in your efforts to save your pet. Other factors include quality of life issues, the logistics of taking your pet to a distant city, the side effects of treatment, other diseases the patient may have, and the prognosis for the different types of cancers.