Page 191 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

170 PART III Therapeutic Modalities for the Cancer Patient

treatment with PDT. An early description of chloro-aluminum The use of intraoperative or perioperative chemotherapy 66,67 is
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sulfonated phthalocyanine–based PDT in 10 cats with superficial receiving increased attention and could have greater implications
for wound healing. Neoadjuvant chemotherapy is also becoming
SCC or carcinoma in situ reported a 70% complete response rate,
VetBooks.ir demonstrating the potential for PDT as a skin cancer treatment. more popular and in some instances may greatly facilitate excision
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With a number of recent technologic improvements, PDT has
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of a solid tumor.
the potential to become integrated into the mainstream of cancer
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treatment. Surgery and Radiation Therapy
Electrochemotherapy Theoretically both preoperative and postoperative RT have advan-
tages. 61,69 Regardless, RT results in some impairment of wound
Electrochemotherapy (ECT) is the use of chemotherapeutic healing potential, and the timing of surgery and RT must be con-
drugs, most typically bleomycin or cisplatin, in combination sidered. Radiation damage to normal tissues (stem cells, blood
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with electric pulses that cause reversible permeabilization of the vessels, lymphatics) may be progressive and potentially permanent
cell membrane, enabling the entry of drugs into the cells (or elec- as the total radiation dose, dose per fraction, and field size increase;
troporation). 43,44 The antitumor effects of ECT are multiple therefore close collaboration between the radiation oncologist and
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and include immunogenic cell death, resulting in eradication of the surgeon is critical in designing the most effective regimen. If
clonogenic tumor cells. More recently ECT has been combined RT is given preoperatively, surgery can be performed after any
with different immunotherapies, especially gene electrotransfer acute radiation effects have resolved (generally 3–4 weeks). Post-
of interleukin-12, to enhance the systemic antitumor effects of operative RT is recommended 7 to 14 days after surgery to allow
ECT. 46–49 Treatment-related adverse effects are usually mild and adequate wound healing. In spite of the theoretical problems, sur-
include wound dehiscence. gery can often be safely performed on irradiated tissues and com-
ECT is indicated primarily for the treatment of incompletely plications are not prohibitive.
excised cutaneous and subcutaneous tumors, but also for the The benefit of surgery and RT is clear for some tumor types;
sole treatment of small primary tumors. Most published studies however, in some instances the improvement in outcome over
are uncontrolled and retrospective in design; however, ECT has single-modality therapy is controversial. Canine nasal tumors
shown some efficacy in the treatment of canine mast cell tumors are one example of this controversy. 71,72 Early reports showed no
(MCTs), 48–53 canine perianal adenomas and adenocarcinomas, 54,55 benefit of surgery and postoperative RT over RT alone; however,
canine nasal tumors, canine and feline localized lymphoma, a recent study demonstrated that preoperative RT was beneficial
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and canine and feline spontaneous soft tissue sarcomas. 58,59 when exenteration of the nasal cavity was performed 6 to 10 weeks
In one study 37 dogs with incompletely excised cutaneous after completion of RT. With the advent of stereotactic radia-
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MCTs were treated with cisplatin ECT; the local recurrence rate tion therapy (SRT) and IMRT (see Chapter 13), such approaches
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was 16%, with a median time to local recurrence of 1200 days. are even more attractive because the overlying skin or underlying
In another study 28 dogs with incompletely excised cutaneous mucosa can be spared the full effects of radiation, thereby dimin-
MCTs were treated with bleomycin ECT; the local recurrence rate ishing concerns about incisional healing after RT. In the past sur-
was 18%, with a median time to local recurrence of 52.8 days. geons were reluctant to operate in a radiation field; these more
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In a retrospective comparative study 51 dogs with cutaneous focused forms of RT hopefully will allow the surgeon to oper-
MCTs were divided into four groups: ECT only, ECT applied ate with fewer wound healing complications and to create novel
intraoperatively, ECT applied postoperatively, and ECT applied treatment plans that combine RT and surgery for select tumors.
for recurrent MCTs. Objective responses were reported in all Radiation side effects are greatly diminished with a more confor-
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dogs with complete responses (CRs) recorded in 93%, 90%, 80%, mal approach, and this in turn makes owners more willing to have
and 64% of dogs treated with ECT postoperatively, intraopera- their pets undergo RT.
tively, alone, and for recurrent disease, respectively. Access to more sophisticated radiation techniques, such as SRT
In one study, of 21 dogs with primary nasal tumors, 11 dogs and IMRT, is rapidly increasing, and with these developments a
were treated with minimally invasive ECT and 10 dogs were new paradigm is emerging in veterinary radiation oncology. For
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treated with cytoreductive surgery and chemotherapy. Partial example, bone sarcomas in locations not amenable to limb-spar-
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and CRs were reported in 64% and 27% of dogs treated with ing surgery now can be treated with curative-intent therapy,
ECT, respectively. Dogs treated with ECT had significantly bet- and treatment protocols for large solid tumors previously deemed
ter 12- and 32-month survival rates (60% and 30%, respectively) nonresectable are being investigated. Combinations of SRT and
than dogs treated with surgery and chemotherapy (10% and 0%, surgery also are being explored.
respectively). Although these new treatment options represent great advances,
familiar challenges remain. In the case of dogs with appendicular
Surgery and Chemotherapy osteosarcoma, fracture may occur after SRT. In addition, although
some of these cases are amenable to surgical stabilization, postop-
The combined use of chemotherapy and surgery is becoming erative infection rates are very high with the presence of orthope-
more commonplace in veterinary oncology, and the knowledge an dic implants, and healing of the fracture does not occur because
oncologic surgeon must possess to master the use of combination of the effects of RT on bone healing. Thus the role of the surgeon
therapy is ever expanding. 60,61 Many chemotherapeutic agents continues to evolve in the management of cases treated with RT.
impede wound healing to some extent. In spite of this risk, few
clinically relevant problems occur when surgery is performed on Prevention of Cancer
a patient receiving chemotherapy. 62,63 General recommendations
are to wait 7 to 10 days after surgery to begin chemotherapy, espe- Certain common cancers in dogs and cats can be prevented. The
cially for high-risk procedures such as intestinal anastomosis. recent elucidation of the canine genome as it relates to genetic
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