A Stratification System for Evaluating and Selecting

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CORRESPONDENCE
756
A Stratification System for Evaluating and Selecting Therapies in Patients With Relapsed or Primary
Refractory Acute Myelogenous Leukemia
To the Editor:
Several characteristics have been predictive of outcome of therapy
for relapsed or “primary refractory” acute myelogenous leukemia
(AML).’-4Among these are duration of first complete remission (CR)
and the number of, and response to, prior salvage regimens. Using
these covariates, we have developed a system that stratifies patients
by probability of response to previous salvage agents. This system
may be useful when comparing new salvage regimens and when
considering which patients might be candidates for phase I studies.
The system is based on analysis of outcome (CR or not) in 206
patients (median age, 56 years) who received chemotherapy without
transplantation for relapsed or primary refractory AML, excluding
acute promyelocytic leukemia (APL), at M.D. Anderson between
1991 and 1994. For first salvage, 68% of the patients received conventional regimens (principally high-dose ara-C-based), and the remaining 32% received investigational regimens (usually single
agents such as topotecan, 2 CDA, CI 973, or taxol). The overall CR
rate was 23%. Ninety-three of the 206 patients received a second
salvage attempt either at second relapse or after failing to respond
to the first attempt. Forty-three percent of the 93 received conventional and 57% received investigational regimens; the overall CR
rate was 1 I %. Forty patients received a third and 17 patients received
a fourth salvage regimen, with CR rates of 10%and 6%, respectively.
The system recognizes four groups: (1) patients with an initial
CR duration in excess of 2 years who are receiving their first salvage
attempt (15 patients; CR rate, 73%; 95% confidence interval [CI],
45% to 92%); (2) patients with an initial CR duration of 1 to 2 years
who are receiving their first salvage attempt (30 patients; CR rate,
47%; 95% CI, 28% to 66%); (3) patients with a first CR lasting less
than 1 year, or with no initial CR, who are receiving their initial
salvage attempt (160 patients; CR rate, 14%; 95% CI, 8% to 21%);
and (4) patients with an initial CR under 1 year, or with no initial
CR, who are receiving a second or subsequent (up to and including
a fourth) salvage regimen, having not responded to a first salvage
attempt (58 patients; 96 salvage attempts; CR rate, 0%; 95% CI, 0%
to 4%). Other patients, eg, those who responded on a first salvage
attempt and who proceed to a second salvage regimen, are excluded
from consideration because of small numbers, although there are
suggestions that patients who respond to the first regimen may be
relatively responsive to the second (3/7 CRs if first CR duration was
I to 2 years; 2/13 if it was shorter). The system was similarly
effective in stratifying the 137 patients who received both initial and
salvage therapy at M.D. Anderson and the 69 patients who were
referred in relapse (49% of whom had received 2 1 regimen for
relapse before referral), with CR rates of 8 of 1 I , 1 1 of 24, 11 of
102, and 0 of 80, and 3 of 4, 3 of 6 , 12 of 58, and 0 of 18 for the
4 groups in the M.D. Anderson and referred categories, respectively.
Considering only patients who received conventional (eg, HDAC,
anthracycline, and mitoxantrone + etoposide) regimens, CR rates
were 11 of 14, 14 of 22, 21 of 104, and 0 of 44, respectively, in
the four groups. Applied prospectively to the 64 salvage AML,
non-APL patients treated without transplantation since 1995, the
scheme’s four groups had CR rates of 3 of 3, 4 of 14, 4 of 33, and
0 of 19, respectively. Tested in patients treated from 1986 through
1989, CR rates were 8 of 11, 13 of 30, 23 of 135, and 0 of 74 in
groups 1 through 4, respectively.
Systems including more covariates, eg, cytogenetics, have been
examined. Not only is complexity increased, but also general applicability may be decreased. Equally importantly, as more covariates
are included, the ability of a prognostic system to stratify future
patients often decreases (“overfitting”).’ Such was the case when
more complex models based on our 1991 through 1994 data were
applied to 1995 and 1996. We use the four-group system described
above both to guide therapy and to compare new salvage regimens.
Patients in group 1 (mean CR rate with prior therapies, about 70%)
receive similar anthracycline + ara-C-based regimens as newly
diagnosed patients, whom they resemble prognostically. In contrast,
patients in group 4 (mean CR rate, < 1%) receive phase I agents.
Phase I1 studies are conducted separately (but simultaneously) in
patients in groups 2 (mean CR rate, 40%) and 3 (mean CR rate,
10%to 20%). Among the advantages of this method are (1) reduction
in the heterogeneity that results if patients in groups 2 and 3 (or
patients in groups 2, 3, and 4) are taken as one group, as is common
practice? with heterogeneity increasing the chances of falsely negative or falsely positive results when testing new agents; and (2)
formal definition of a group (group 2) that may be sufficiently favorable prognostically to avoid the false-negative that presumably results if new regimens are only examined in the least “favorable”
patient^.'.^.' Although randomized phase 11 designs have been proposed to reduce heterogeneity among groups of patients treated with
different agents,’ the sample sizes envisioned in these designs are
insufficient for this purpose in the absence of stratification, using a
system such as that proposed above. Although the need to test new
agents separately in different strata potentially increases phase II
sample size, Bayesian pre-phase I1 selection designs effectively address the issue of sample size.’ We believe these designs together
with the stratification system outlined here represent improvements
in methodology for testing new agents in AML.
Elihu Estey
Steven Komblau
Sherry Pierce
Hagop Kantarjian
Miloslav Beran
Michael Keating
Leukemia Section
University of Texas M.D. Anderson Cancer Center
Houston, TX
REFERENCES
I . Keating MJ, Kantarjian H, Smith TL, Estey E, Walters R,
Anderson B, Beran M, McCredie KB, Freireich EJ: Response to
salvage therapy and survival after relapse in acute myelogenous
leukemia. J Clin Oncol 7:1071, 1989
2. Hiddemann W, Martin WR, Sauerland CM, Heinecke A, Biichner T: Definition of refractoriness against conventional chemotherapy in acute myeloid leukemia: A proposal based on the results of
retreatment by thioguanine, cytosine arabinoside, and daunorubicin
(TAD 9) in 150 patients with relapse after standardized first line
therapy. Leukemia 4: 184, 1990
3. Angelov L, Brandwein JM, Baker MA, Scott G , Sutton DM,
Keating A: Results of therapy for acute myeloid leukemia in first
relapse. Leuk Lymphoma 6:15, 1991
4. Estey E: Treatment of refractory AML. Leukemia (in press)
Matchar DB, Reichert TA: Regression
5. Harrell FE Jr, Lee IU,
models for prognostic prediction: Advantages, problems, and suggested solutions. Cancer Treat Rep 69:1071, 1985
6 . Simon R: Importance of prognostic factors in cancer clinical
trials. Cancer Treat Rep 68: 185, 1984
7. Simon R, Wittes RE, Ellenberg SS: Randomized phase 11clinical trials. Cancer Treat Rep 69:1375, 1985
8. Thall PF, Estey E H A Bayesian strategy for screening cancer
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From www.bloodjournal.org by guest on February 6, 2015. For personal use only.
1996 88: 756
A stratification system for evaluating and selecting therapies in
patients with relapsed or primary refractory acute myelogenous
leukemia [letter]
E Estey, S Kornblau, S Pierce, H Kantarjian, M Beran and M Keating
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