5. Results
5.2 Response and toxicity
Forty-six dogs achieved CR, and 19 dogs achieved PR. No response to treatment
was observed in 4 dogs. Total response rate (CR + PR) was 94%. Median time to tumor
progression (TTP) was 185 days (range, 16-831 days). Median overall survival time
(OST) was 282 days (range, 32-841 days). Kaplan-Meier curves of TTP and OST are
shown in Figure 1~2.
Forty-eighty (69.6%) dogs were dead due to lymphoma. Five (7.2%) dogs were
euthanized due to lymphoma progression. Two (2.9%) dogs were dead after seizure and
lymphoma involvement was highly suspected. Nine (13%) dogs lost follow-up, with
median and mean follow-up time 518 and 795 days, respectively. Three (4.3%) dogs
were still alive at the end of the study, with follow-up time 1318, 1745, and 2358 days,
respectively.
Twenty-four dogs (35%) finished the first two cycles less than 80 days, whereas 40
(58%) dogs more than 80 days. Five (7%) dogs were dead due to lymphoma or severe
chemotherapy toxicity before finishing the first two cycles.
Toxicity profile was presented as the number of patients experienced certain type
of toxicity of certain grade, as listed in Table 6~7. The protocol was generally well
tolerated. Anorexia, vomiting, and diarrhea of grade 4, which necessitated
hospitalization, occurred in only 0 (0%), 1 (1%), and 2 (3%) dogs, respectively.
Neutropenia of more than grade 1.1, which necessitated treatment delay, occurred in 47
(50%) dogs, whereas grade 2 and 3 neutropenia occurred in only 10 (15%) dogs. 2 (3%)
dogs were dead due to chemotherapy toxicity.
5.3 Prognostic factors
Age, WHO clinical stage, presence of anemia at diagnosis, response to treatment,
and time to finish the first two CHOP cycles were identified as significant for TTP. Age,
WHO clinical stage, WHO clinical substage, presence of anemia at diagnosis, response
to treatment, and time to finish the first two CHOP cycles were identified as significant
for OST. More than 10 years old was related to worse outcome. WHO clinical stage III,
WHO clinical substage a, absence of anemia at diagnosis, and finishing the first two
cycles >80 days were associated with better outcome. Patients in the three categories of
response to treatment exhibited different outcome, with CR being the best and NR being
the worst. Median TTP and OST and P values according to above factors are provided
in Table 8. Kaplan-Meier curves for TTP and OST of above factors are demonstrated in
Figure 3~14.
Immunophenotype was available for only 24 (35%) dogs. Presence of
hypercalcemia at diagnosis, and pre-treatment with steroid were only noted in 2 (3%)
and 8 (12%) dogs. These three factors were excluded from analysis due to low case
numbers.
5.4 Long-term analysis
In the 154 groupings, statistical significance was found in 9 and 15 groupings for
TTP and OST, respectively. All P values for TTP and OST of the 154 groupings are
provided in Table 9. To best illustrate these results, some groupings were selected and
compared in order to elucidate the influences of the five variables (form of toxicity,
timing during the protocol, drug, toxicity grade, frequency) on the correlation between
toxicity and efficacy.
Form of toxicity and toxicity grade
Table 10 included P values for 15 groupings which set timing during the protocol
as full course, drugs as all drugs, and frequency as at least once (ie, first, second and
fifth digit of coding system fixed to 1). In other words, these 15 groupings focused on
only form of toxicity and toxicity grade, neglecting the other three variables. The
continued part of Table 10 is composed of groupings dividing patients into three groups,
and the exact P values between each group are provided in Table 11.
Based on results of grouping 11110, patients who experienced neutropenia of more
than grade 1.0 (ie, neutrophil <5000 µl) had longer OST (P =0.045) than patients who
did not experience any episode of neutropenia, whereas there was no difference in TTP
(P =0.094). If shifting definition of occurrence of toxicity to neutropenia of more than
grade 2 (ie, neutrophil <1500 µl), as in grouping 11130, differences could be only
observed in the Kaplan-Meier curve for OST (Figure 16), but no statistical significance
was detected in either TTP (P =0.151) or OST (P =0.063). If dividing patients into no
toxicity, low-grade toxicity (grade 1.0 and 1.1) and high-grade toxicity (grade 2 and 3),
as in grouping 11140, statistical difference was found in OST (P =0.044), with actually
only low-grade toxicity group superior to no toxicity group (P =0.039) and high-grade
toxicity group superior to no toxicity group (P =0.005), but no significant differences in
low-toxicity group and high-toxicity group (P =0.055). The Kaplan-Meier curves for
OST for the three neutropenia groupings were demonstrated in Figure 15~17.
Groupings with first digit assigned as 2 examined anorexia and efficacy. The three
anorexia groupings (21110, 21130, and 21140) in Table 10 were all statistical
insignificant. In fact, no statistical significance was found in any anorexia groupings in
the study.
Groupings with first digit assigned as 3, 4, and 5 focused on vomiting, diarrhea and
combined GI signs. In groupings 31110, 41110, and 51110, toxicity of any grade was
considered as occurrence of toxicity, and statistical significance was found in vomiting
and combined GI signs, but not diarrhea, for TTP (P =0.042 and 0.007) and OST (P
=0.023 and <0.001). If shifting definition of occurrence of toxicity to toxicity of more
than grade 3, as in groupings 31130, 41130, and 51130, differences were only detected
in diarrhea groupings for both TTP (P =0.034) and OST (P =0.017), and in contrary to
the study’s hypothesis of toxicity improving efficacy, patients who experienced diarrhea
of more than grade 3 exhibited poorer outcome. The Kaplan-Meier curves of the above
groupings with P value <0.05 were shown in Figure 18~23. After dividing patients into
no toxicity, low-grade toxicity (grade 1 and 2) and high-grade toxicity (grade 3 and 4),
as in grouping 31140, 41140, and 51140, statistical significance was found in diarrhea
and combined GI signs for TTP (P =0.015 and 0.017) and OST (P =0.004 and 0.001),
and in vomiting for OST (P =0.04). Looking into the Kaplan-Meier curves, as shown in
Figure 24~29 for these groupings, one can tell that low-toxicity groups performed
better than no toxicity groups, but high-toxicity groups diminished the favorable
prognostic value of toxicity, leading to similar or worse outcome comparing to no
toxicity or low-grade toxicity groups. Detailed intergroup P values for those groupings
are provided in Table 11. Patients with high-grade vomiting or combined GI signs had
similar outcome to patients with low-grade vomiting or combined GI signs, although
poorer outcome in high-grade toxicity group could be subjectively observed in the
Kaplan-Meier’s curves; Patients with high-grade diarrhea had poorer outcome than both
patients with low-grade diarrhea and no diarrhea.
Timing during the protocol
No groupings focusing on only toxicities appeared in the first two cycles of the
protocol (ie, the second digit assigned as 2) showed statistical significance.
Drugs
Among groupings that focusing on particular drug (ie, the third digit assigned as 2,
3, or 5), statistical significance was found for TTP and OST in grouping 11310 (P
=0.042 and 0.019), 41230 (P =0.022 and 0.015), and 41240 (P =0.031 and 0.014), and
for only OST in grouping 51210 (P=0.03). The results of grouping 11310 suggested that
patients who experienced neutropenia of more than grade 1.0 after cyclophosphamide
had better outcome. The results of grouping 41230 and 41240, which defined
occurrence of toxicity as diarrhea of more than grade 3 after vincristine or divided
patients into 3 groups according to diarrhea grading after vincristine, were similar to the
results of diarrhea groupings in the previous section: diarrhea of high grade was
associated with poorer outcome. The results of grouping 51210 suggested that patients
who experienced anorexia, diarrhea, or vomiting of more than grade 1 after vincristine
had longer OST, but not TTP. The Kaplan-Meier curves for these four groupings with P
value <0.05 were provided in Figure 30~36.
Frequency
Among groupings that examined if frequency of toxicity is a determinant (ie, the
fifth digit assigned as 3 or 5), statistical significance was found for OST in grouping
31113 (P =0.015) and 31143 (P =0.014), and for TTP and OST in grouping 41143 (P
=0.045 and 0.019). The results of these three groupings were similar to their
non-frequency-adjusting counterparts (ie, 31110 for 31113, 31140 for 31143, and 41140
for 41143): In grouping 31113, patients who experienced vomiting of any grade more
than three times exhibited better outcome, as in grouping 31130; In groupings 31143
and 41143, patients who experienced vomiting or diarrhea of grade 1 or 2 more than
twice had better outcome than patients who did not experience vomiting or diarrhea
more than twice, but patients who experienced vomiting or diarrhea of grade 3 or 4
low-grade toxicity group, as in grouping 31140 and 41140. Table 12 listed P values of
the three above-mentioned groupings and their no frequency-adjusting counterparts.
Figure 37~40 showed the Kaplan-Meier curves with P value <0.05.
For all grouping with P value <0.05, excluding drug-specific groupings (ie, the
third digit assigned as 2, 3, or 5) and frequency-adjusting groupings (ie, the fifth digit
assigned as 3 or 5), chia-square test was performed to examine the correlation between
grouping and significant prognostic factors. Age, response to treatment and anemia
were found to be associated with some of these groupings: Age was correlated to
grouping 31110, 31140, 41140, 51110, and 51140 (P =0.015, 0.016, 0.016, 0.028, and
0.009); Response to treatment was correlated to grouping 11110, 11130, 31110, 41110,
51110, and 51140 (P =0.004, <0.001, 0.006, 0.001, < 0.001, and 0.001); Anemia was
correlated only to grouping 11310 (P =0.022). P values and percentages of the above
comparisons, are listed in Table 13~15. As demonstrated in Table 13~14, more than 10
years old was associated with lower percentage of toxicity in grouping 31110, and
lower percentage of low-grade toxicity in grouping 31140, 41140, and 51140, whereas
CR was related to higher percentage of toxicity in grouping 11110, 31110, and 51110,
higher percentage of low-grade toxicity in grouping 41140 and 51140, and higher
percentage of both low-grade and high-grade toxicity in grouping 11140. These results
indicated that the connections found was plausible: More than 10 years old, a negative
prognostic factor, was with less patients in the favorable toxicity group; CR, a positive
prognostic factor, was with more patients in the favorable toxicity group.
In multivariate analysis, all groupings with P value <0.05, excluding drug-specific
groupings and frequency-adjusting groupings, and all significant prognostic factors
were included for Cox regression. For both TTP and OST, WHO clinical stage, time to
finish the first two cycles of the protocol, and grouping 11140 (ie, neutropenia, dividing
into no toxicity, low-grade toxicity and high-grade toxicity groups) remained statistical
significance (P <0.001, =0.011, and 0.008 for TTP; P <0.001, = 0.002, and 0.001 for
OST).
5.5 Short-term analysis
In short-term analysis for neutropenia, statistical differences were detected in
comparisons including treatment with all drugs (P =0.008) and with only vincristine (P
=0.013). Odds ratio of the odds of effective treatment to ineffective treatment were 0.33
and 0.23, respectively, demonstrating that with occurrence of neutropenia, effective
treatment was more likely to happen than ineffective treatment.
In short-term analysis for combined GI signs, statistical differences were detected
in comparisons including treatment with all drugs, with vincristine, or with
cyclophosphamide (P <0.001, <0.001, and =0.003). Odds ratio of the odds of effective
treatment to ineffective treatment were 0.53, 0.56, and 0.42, respectively, demonstrating
that with occurrence of GI toxicity, effective treatment was more likely to happen than
ineffective treatment.
Table 16 listed all the P values and odds ratios in the short-term analysis.