Page 1295 - Small Animal Internal Medicine, 6th Edition

CHAPTER 75 Principles of Cancer Treatment 1267

or dog with cancer receiving treatment. Our motto is “The BOX 75.2
patient should feel better with the treatment than with the
VetBooks.ir disease.” Criteria Used to Assess Tumor Response to Treatment in
Cancer treatment can be either palliative or curative.
Pets With Lymphoma
Given the current paucity of information regarding specific
tumor types and treatments, these two approaches some- Complete Response (CR):
times overlap (i.e., a treatment initially thought to be pallia- Target lesions: Disappearance of all evidence of disease.
tive may result in cure, or vice versa). As discussed earlier, All lymph nodes must be nonpathologic in size in the judg-
every effort should be made to eradicate every single cancer ment of the evaluator(s).
cell in the body (i.e., obtain a cure) shortly after diagnosis, if Nontarget lesions: Any pathologic lymph nodes must be
“the price is right” (i.e., the cost and toxicity are not excessive considered to have returned to normal size in the judgment
of the evaluator(s), and no new sites of disease should be
and the patient’s QOL will be good). This means taking observed. Spleen and liver should be considered within
immediate action rather than adopting a wait-and-see atti- normal limits by the evaluator(s).
tude. With few exceptions, malignant tumors do not regress
spontaneously. In other words, by delaying treatment in a Partial Response (PR):
patient with confirmed malignancy, the clinician is only Target lesions: At least a 30% decrease in the mean sum
increasing the probability that the tumor will disseminate LD of target lesions taking as reference the baseline mean
locally or systemically, thereby decreasing the likelihood of sum LD. Nontarget lesions: Not applicable.*
a cure. As discussed earlier, surgery and radiotherapy are Progressive Disease (PD):
potentially curative treatments, whereas chemotherapy and
immunotherapy are usually palliative. Target lesions: At least a 20% increase in the mean sum
If a cure cannot be obtained, the two main goals of treat- LD taking as reference the smallest mean sum LD at baseline
ment used to be to induce remission while achieving a good or during follow-up (this includes the baseline mean sum
LD if that is the smallest on study). The LD of at least one
QOL. The term remission refers to shrinkage of the tumor. of the target lesions must demonstrate an absolute increase
When objectively evaluating the effects of therapy, the clini- of at least 5 mm compared with its nadir for PD to be
cian should measure the tumor or tumors and assess the defined. For target lesions less than 10 mm at nadir, an
response using the criteria given in Box 75.2. Recently, vet- increase in LD of any single previously identified target
erinary oncologists adopted RECIST (response evaluation lesion to 15 mm or greater.
criteria in solid tumors), commonly used in people (Eisen- Nontarget lesions: unequivocal progression of existing
hauer et al., 2009), and have adapted them to lymphomas nontarget lesions, in the judgment of the evaluator. (Note:
(Vail et al., 2010). The appearance of one or more new lesions is also con-
A newer approach that may become more and more sidered progression.)
common as data are generated is the use of novel, low-dose Stable Disease (SD):
treatment (metronomic chemotherapy) to “keep the tumor Target lesions: Neither sufficient decrease to qualify for PR
at bay” while preserving the patient’s QOL. Most cancer nor sufficient increase to qualify for PD. Nontarget lesions:
patients are not symptomatic when they first present; hence Not applicable.*
keeping the tumor as-is while preserving the QOL is a viable
(and attractive) option for an elder patient. Metronomic che- LD, Longest diameter.
motherapy is discussed in detail in Chapter 76. This is a modification of the RECIST criteria (Eisenhauer et al.,
The QOL issue is important in small animal oncology (see 2009) and can be applied to pets with solid tumors.
preceding paragraphs). In a QOL survey of owners whose Modified from Vail DM, et al.: Response evaluation criteria for
peripheral nodal lymphoma in dogs (v1.0)—a Veterinary
pets had undergone chemotherapy for nonresectable or met- Cooperative Oncology Group (VCOG) consensus document, Vet
astatic malignancy conducted in the author’s clinic, more Comp Oncol 8:28, 2010.
than 80% responded that the QOL of their pets was main- *Nontarget lesions will be assessed as “CR,” “PD,” “non-CR/
tained or improved during treatment. If a good QOL cannot non-PD,” or, if there are no nontarget lesions, “None.”
be maintained (i.e., the patient’s performance status deterio-
rates), the treatment should be modified or discontinued.
Several useful QOL evaluation tools have been developed for palliative surgery (e.g., in dogs or cats with ulcerated
use in pets with cancer (Lynch et al., 2011). mammary carcinomas and small pulmonary metastases,
Palliative treatments are acceptable for small animals with euthanasia is frequently recommended because the primary
cancer and to their owners. For example, even though che- lesion is draining and thus does not allow for the patient to
motherapy rarely achieves a cure for most tumors, veterinar- be a “pet,” as in sitting on the owners’ lap or on the furniture).
ians can provide a cat or dog (and its family) with a prolonged, Clinicians now know that performing a mastectomy or
good-quality survival. Although these patients ultimately die lumpectomy (even if the owners decline chemotherapy) is
of tumor-related causes, the owners are usually pleased to likely to result in several months of good-quality survival,
have a pet that is asymptomatic for a longer period of time. until the metastatic lesions finally cause respiratory compro-
Another common example that is frequently forgotten is mise. In another example, dogs with apocrine gland