Page 190 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 10 Surgical Oncology 169

decision of when to discontinue therapy. One of the most difficult and secondary hepatic tumors. The minimally invasive nature
decisions in surgical oncology is the decision not to operate. Treat- of this technique makes it ideal for the treatment of metastatic
liver lesions. For the treatment of metastatic colorectal cancer to
ment of any kind should never be worse than no treatment.
VetBooks.ir eficial. Examples include mastectomy for infected, metastatic the liver, RF has 5-year survival rates similar to those for surgery.
However, in many situations palliative surgery may be ben-
Microwave ablation is similar to RF, but higher frequency currents
mammary tumors; anal sacculectomy for dogs with a large local (900–2459 MHz) are delivered. Microwave ablation is a newer
AGASAC causing tenesmus and distant metastasis; and splenec- technology with less evidence supporting its use, but it is often
tomy for a dog with a ruptured splenic tumor. used for the same indications as RF ablation. RF and microwave
ablation have been reported in dogs as experimental models. 27,28
Cytoreductive Surgery
Cryoablation
Incomplete removal of a tumor (planned or unplanned), in which
gross tumor is left behind, is referred to as intralesional, debulk- Cryosurgery, or cryoablation, is a much older form of local ther-
ing, or cytoreductive surgery. It is commonly performed but rarely apy that has local anticancer effects by means of direct cell kill and
indicated. A theoretical indication is to enhance the efficacy of vascular collapse. It has been used extensively in veterinary medi-
23
other treatment modalities; for example, debulking an infiltrative cine, most commonly for skin, nasal planum, eyelid, perianal, and
lipoma in a swollen limb before RT. Debulking is a practical con- oral cavity tumors. 29–31 Cryotherapy continues to be an attractive
sideration before cryosurgery to reduce the amount of tissue to treatment option for owners not interested in invasive procedures
freeze and the duration of the cryotherapy. Cytoreduction may and for palliation of advanced (i.e., nonresectable or metastatic)
also help with treatment planning and dosimetry for certain types oral tumors. Cryotherapy can be used as an adjunct to cytoreduc-
of RT. However, the improved tumor control achieved is more a tive surgery. There is one report of image-guided cryoablation of
result of geometric and dosimetry considerations than intentional a nasal mass in a dog that recurred after intensity-modulated RT
32
and incomplete removal of tumor cells. Removing 99.9% of a 1 (IMRT). In humans laparoscopic and percutaneous cryoabla-
cm tumor (1 × 10 , or 1 billion cells) still leaves a million resid- tion of select neoplasms (e.g., breast and renal tumors) has become
9
ual cancer cells. Immunotherapy and chemotherapy theoretically an attractive, minimally invasive treatment option. 33,34
could be helped by reducing tumor volume (e.g., LN removal for
oral melanoma with the use of a melanoma vaccine), 24,25 but to Hyperthermia
date few well-controlled clinical trials have shown a benefit in vet-
erinary medicine. If tumors are debulked with the anticipation Hyperthermia is the elevation of tissue temperature above nor-
of postoperative RT, the margins of debulked tumor should be mal physiologic levels. The term hyperthermia encompasses a wide
marked with radiopaque metal clips to allow proper treatment range of temperatures and modalities. A variety of methods and
planning based on radiographs or CT of the surgical site. The ori- devices are used clinically to induce hyperthermia in tissues. Non-
entation of the incision should be considered carefully if RT is invasive methods using RF currents, microwaves, or ultrasound
possible postoperatively. are the most common. Heating of solid tumors typically is non-
uniform because of the heating devices available, nonuniform dis-
Nonsurgical Locally Ablative Procedures tribution of blood flow in the tumor, and heat-dissipating activity
of adjacent normal tissue. A number of studies demonstrated an
Ablative techniques to eradicate local (or metastatic) disease have improved outcome when hyperthermia was combined with RT
a place in oncology, but they are based only rarely on evidence of for the treatment of solid tumors in dogs. 35–38 The ideal strategy
26
outcomes. Indications for the use of local ablative therapy vary, for clinical hyperthermia treatment, including thermal dose, frac-
but they generally are limited to small, discrete lesions <2 cm. A tionation, and time and temperature goals, has yet to be identified.
limitation of all these techniques is that completeness of cell kill
and margin analysis cannot be determined after treatment. If the Photodynamic Therapy
operator picked the correct tumor, site, and dose delivery, then
local control may be achieved; however, monitoring for regrowth The practice of using sunlight to treat disease is ancient, but mod-
is the only way to ensure that treatment has been adequate. As a ern refinements have allowed the interactions between light and
general rule, recurrent disease tends to be more invasive and dif- drugs to evolve into a highly effective cancer treatment called
ficult to control than primary disease, so the first ablative proce- photodynamic therapy (PDT). PDT relies on light of an appro-
dure should be well planned and executed. All of the local ablative priate activating wavelength, oxygen, and a photosensitizer (PS)
treatments require special equipment and training to be performed that accumulates within a tumor. The excited PS interacts with
properly. Selective tumor cell kill that spares adjacent normal tis- molecular oxygen, creating reactive oxygen species that are respon-
sue is often claimed for these techniques, but it is unlikely to be sible for causing vascular stasis and necrosis, membrane damage,
consistently true. and apoptosis, and for initiating a signaling cascade resulting in
an influx of inflammatory cells. Although initially studied as a
Radiofrequency Ablation single modality, PDT may also be useful when combined with
other cancer treatments. Early studies show that a combination
The most common nonsurgical locally ablative procedures in of PDT and low-dose cisplatin increased efficacy in both in vitro
human medicine include radiofrequency (RF) ablation, micro- and murine models, and similar synergy has been observed when
wave ablation, and cryoablation. RF ablation involves delivery of doxorubicin is combined with PDT. 39,40 In veterinary medicine
a high-frequency (300–500 KHz) alternating current via a needle- PDT most commonly has been used in the treatment of feline
like probe. The procedure typically is performed with either ultra- squamous cell carcinoma (SCC). Most SCCs are superficial,
sound or CT guidance and is commonly used to treat primary localized, and rarely metastasize, making them well suited for