Follow-Up of Complete Cytogenetic Remission in Patients With Chronic Myeloid Leukemia After Cessation of Interferon Alfa
From the Service des Maladies du Sang, Centre Hospitalier Universitaire de Bordeaux, and Université Victor Segalen Bordeaux 2, Bordeaux; and Hôpital Haut-Levêque, Pessac, France.
Address reprint requests to J. Reiffers, MD, Université Victor Segalen, Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux, France; email: president@u-bordeaux2.fr.
ABSTRACT
PURPOSE: A small proportion of patients with chronic myeloid leukemia (CML) achieve a complete cytogenetic response (CCR), defined as the disappearance of Philadelphia (Ph) chromosome-positive metaphases, after treatment with interferon alfa (IFN). In this population of patients, the question of whether treatment should then be withdrawn is not yet resolved.
PATIENTS AND METHODS: In the present study, we followed 15 patients who stopped IFN after achieving CCR. In nine patients IFN was stopped in view of adverse reactions (n = 8) or patient's choice (n = 1). For the remaining six patients, the treatment was stopped because no BCR/ABL rearrangement could be detected by reverse transcriptase polymerase chain reaction (RT-PCR) in four successive analyses using peripheral-blood samples.
RESULTS: Loss of CCR and survival were not statistically different (P = .48; P = .7) for the 15 patients who stopped IFN compared with 41 other CCR patients who continued IFN therapy in our institution. The median follow-up after discontinuation of IFN treatment was 36 months (range, 6 to 108 months). Seven patients (47%) (females, or CCR > 24 months and RT-PCR negative before IFN cessation; P < .0001) did not relapse. Eight other patients (53%) relapsed (lost CCR) within 3 to 33 months of treatment discontinuation. One of them relapsed in major cytogenetic remission (MCR) and was still in MCR 87 months after stopping therapy without any treatment.
CONCLUSION: It is possible to stop IFN treatment at least in some patients with CML who achieve a prolonged period of CCR. This study also illustrates the hypothesis that persistence of low numbers of Ph-positive cells does not necessarily imply hematologic relapse.
INTRODUCTION
CHRONIC MYELOID Leukemia (CML) is a clonal myeloproliferative disorder characterized by acquisition of the Philadelphia chromosome (Ph) in leukemic stem cells and their progeny.1,2 The abnormal Ph chromosome is the result of a reciprocal translocation between chromosomes 9 and 22. The major consequence of this translocation is the fusion of the ABL gene to the BCR gene on chromosome 22.3 The BCR-ABL fusion gene encodes an oncogenic fusion protein of 190, 210 or 230 kd, depending on the breakpoint on the BCR gene.4
All these Bcr-Abl fusion proteins have an enhanced tyrosine kinase activity, which is critical for the development of the disease.5 The cells belonging to the malignant clone can be detected by either chromosome analysis or molecular techniques designed to monitor (and amplify) the expression of the characteristic Bcr-Abl message.6 The course of CML is characterized by a multistep process from a chronic phase to accelerated and blastic phases with rapidly fatal outcome. Until now, allogeneic bone marrow transplantation has been the curative treatment for CML patients younger than 45 to 50 years.7 Using recombinant interferon alfa (IFN), it has been shown that complete hematologic remission (CHR) and a cytogenetic response (minor, partial, or even complete) can be achieved in some patients with newly diagnosed CML, and that some of these remitter patients have a prolonged survival.8-11 We have already reported the factors influencing survival and the response to IFN to identify early the CML patients who could be proposed for alternative treatments.12 However, IFN therapy is expensive and induces side effects, and it is not known how long IFN can be continued after achieving a complete cytogenetic response (CCR). A new specific drug, STI571, was recently developed for specifically inhibiting the BCR-ABL kinase activity.13 Because the results of the first clinical trials are very promising, it may be speculated that this new compound will probably represent another therapeutic tool.14 In addition, as this drug is able to induce a cytogenetic response, the duration of such a treatment will become a relevant issue.
In the present study, we observed 15 patients who discontinued IFN after achieving a CCR. All the patients with a short CCR (median, 9 months; range, 5 to 19 months) before IFN cessation experienced relapse. One specific patient with a CCR for 35 months experienced relapse after a few months but remained with a low percentage of Ph-positive cells 6 years after cessation of IFN without any other treatment. In contrast, the seven patients with a long period of CCR before cessation (median, 60 months; range, 24 to 84 months) did not relapse. We therefore suggest that it is possible to stop IFN in CML patients after a long period of CCR without relapse.
PATIENTS AND METHODS
Patients and Treatment
Between 1984 and 1998, 238 patients with newly diagnosed Ph-positive CML were treated in our institution with IFN with or without chemotherapy including autologous stem-cell transplantation (ASCT). A total of 56 patients achieved a CCR at least once. The modalities of IFN administration as well as the factors influencing the response to IFN have been reported elsewhere.12
Fifteen of these 56 patients in CCR stopped IFN treatment. Their main characteristics are shown in Table 1. At diagnosis, 14 patients were in chronic phase and one patient was in accelerated phase. The median age was 49.5 years, with a range from 28 to 66 years. According to Sokal's classification, nine patients were low risk (index < 0.8), four were intermediate risk (index 0.8 to 1.2), and two were high risk (index > 1.2) (Table 1). Twelve patients were given recombinant IFN (5 MIU/m2/d, subcutaneously) as first-line treatment. In addition to IFN treatment, two patients received ASCT with peripheral-blood cells collected at diagnosis, because they were considered resistant to IFN during the first period of treatment.15 The patient who was in accelerated phase underwent ASCT as first-line treatment, then was treated with IFN. In all cases, IFN doses were subsequently adjusted to maintain the WBC count between 1.5 and 5 x 109/L and the platelet count between 50 and 150 x 109/L.12
Table 1. Characteristics of 56 Patients Achieving CCR in Our Institution
Response Criteria to IFN
Hematologic and cytogenetic responses were evaluated according to the criteria reported by the Houston group.8 A CHR required the normalization of peripheral WBCs to fewer than 10 x 109/L, with disappearance of immature circulating cells (blasts, promyelocytes, myelocytes, and metamyelocytes), the normalization of platelet count (< 450 x 109/L), and the disappearance of all signs and symptoms of the disease (in particular, palpable splenomegaly). This included patients whose peripheral WBC counts had become normal but who had persistent splenomegaly or immature peripheral cells. Accelerated phase was defined according to the criteria described by Kantarjian et al,16 and blast crisis was considered to have occurred when more than 30% blast cells were present in the bone marrow.
Cytogenetic Evaluation
Bone marrow karyotypes were performed using a routine cell synchronization technique after a 24- to 48-hour culture. Twenty-five to 30 R-or G-banded metaphases were photographed or video-printed. Cytogenetic response was classified according to the proportion of Ph metaphases. Partial response was considered to have occurred when the Ph chromosome persisted in 1% to 34% metaphases. Complete response was documented when the Ph chromosome was not found in marrow metaphases. Partial cytogenetic response and CCR together were considered as major cytogenetic response (MCR).17 Because the study focused on CCR, relapse was defined as the loss of CCR.
Analysis for Bcr-Abl Rearrangement
When CCR was reached, the minimum residual disease was determined by molecular amplification of Bcr-Abl mRNA using reverse transcriptase polymerase chain reaction (PCR) from peripheral-blood samples. This was performed as previously described using a nonquantitative technique with a sensitivity of one leukemic cell for 104 normal cells.18
Statistical Analysis
Quantitative variables were expressed as median and range (minimum to maximum). Comparisons of patients' characteristics between groups were made using the Wilcoxon test for the quantitative variables and the ?2 test or the Fisher's exact test for qualitative variables. Survival and cumulative incidences of CCR were estimated by Kaplan-Meier analysis.
RESULTS
Causes for Discontinuing IFN
Depending on the cause of treatment cessation, the patients were separated in two groups.
Group 1 (nine patients) comprised the eight patients who stopped IFN because severe adverse effects occurred. The different complications were neurotoxicity (two cases), cardiac failure (one case), renal impairment with lupus (one case), hepatitis (one case), and autoimmune disorder (two cases). In this group we included another patient who decided to interrupt IFN for personal reasons.
Group 2 included six patients who stopped IFN because the minimum residual disease was at an undetectable level that was sustained during the follow-up; ie, the reverse transcriptase PCR for Bcr-Abl was negative in our hands during 2 subsequent years on at least four different analyses.
For the 15 patients, the median duration of IFN treatment before cessation was 64 months (range, 22 to 96 months) and the median follow-up after cessation was 36 months (range, 6 to 108 months). The median duration of CCR in the 41 patients who continued IFN therapy was 20.5 months, and the median follow-up was 41.1 months (range, 2 to 130 months).
Effect of Treatment Cessation on Relapse and Survival
Among the 56 patients who achieved CCR in our institution, the characteristics between patients who stopped therapy versus those who continued were the same (Table1). The relapse incidence, ie, the loss of CCR, was not different (P = .48) for the 15 patients who stopped IFN compared with the 41 who continued the treatment (Fig 1). In addition, the overall survival of these two groups was not different (P = .7) (Fig 2). Among the subset who stopped therapy, all of the six patients with CCR lasting less than 2 years experienced relapse (100%), whereas only two (22%) of nine with CCR lasting more than 2 years did (see Prognostic Factors). Therefore, we also analyzed the 56 patients by dividing them in two groups according to the duration of CCR (24 patients < 24 months v 32 patients > 24 months). The different factors such as age, sex, spleen size, WBC, platelet count, peripheral-blood blast cells, peripheral basophil, hemoglobin, and Sokal index were not statistically different in the two groups. Overall survival was not different for those who had a CCR more than 24 months compared with the others (P = .06) (Fig 3)
Fig 1. Probability of being in sustained CCR among the patients who stopped IFN (n = 15) and the other patients (n = 41) (P = .34). The curve is plotted from the moment CCR was obtained.
Fig 2. Overall survival among the CCR patients who stopped IFN (n = 15) and the other patients (n = 41) (P = .7).
Fig 3. Overall survival (n = 56) among the patients who had CCR for 24 months and those who had CCR for less than 24 months.
Outcome of Relapsing Patients
Among the 15 study group patients, eight patients (53%) relapsed within 3 to 33 months of treatment discontinuation. All belonged to group 1. Hematologic relapse was observed in three patients who had an increased proportion of Ph-positive cells preceding hematologic relapse, which was observed at 6, 14, and 72 months after stopping IFN. These three patients were treated with hydroxyurea. One patient progressed to accelerated phase. In another patient, CHR was obtained but death occurred due to respiratory failure (pulmonary fibrosis). The third is still in partial hematologic remission 95 months after stopping IFN (Fig 4).
Fig 4. Evolution and follow-up of patients with hematologic and cytogenetic relapse. Doses of IFN are given per week in million international units (MIU).
Five of the eight patients had a cytogenetic relapse with an increasing percentage of Ph-positive cells, as shown in Fig 4. One patient relapsed at 7 months with reappearance of 4% Ph-positive cells (one among 25 mitoses). The following pattern was then observed: one Ph-positive cell among 31 after 1 year, zero among 28 after 2 years, one among 31 after 3 years, one among 26 after 4 years, and two among 31 mitoses. Therefore, this patient is still in MCR (6% of Ph-positive cells) 75 months after stopping therapy (Fig 4). Four other patients relapsed at 3, 5, 6, and 7 months after IFN withdrawal.
Cytogenetic response was reinduced in these four patients who resumed IFN-based therapy. As shown in Fig 4, cytogenetic responses (one CCR and three MCRs) were obtained after restarting IFN with low doses, ie, those used just before the moment of treatment discontinuation.
Outcome and Follow-Up of Nonrelapsing Patients
Seven patients were still in CCR without further treatment, with a median follow-up of 36 months (range, 6 to 105 months) after IFN withdrawal. One patient (Da) belonged to group 1 and the follow-up is illustrated in Fig 5. This patient stopped IFN after 44 months for cardiac toxicity. He was then in CCR with a very low level of minimum residual disease (four negative PCRs during the 2 years before stopping IFN). The patient was still in CCR 9 years after IFN withdrawal without any kind of treatment. PCR results for Bcr-Abl were variable (three positive tests) during the first 4 years and negative for 5 years.
Fig 5. Follow-up of qualitative PCR for BCR-ABLrearrangement in the patients who did not experience relapse.
There was no relapse in any of the six patients who stopped IFN because the level of residual disease was very low, ie, those belonging to group 2 (Fig 5). The patient who had the shortest follow-up died due to an extrahematologic event (heart arrest). For four patients after IFN withdrawal, the PCR results were sometimes negative and sometimes positive. Conversely, for one patient (Vi) PCR was negative only once during the follow-up. The sustained CCR was confirmed by cytogenetic analysis each time a positive PCR result was obtained.
Prognostic Factors
We divided the 56 CCR patients into those who stayed in continuous CCR (n = 27) versus those who relapsed (n = 29) and analyzed the different factors. Age, WBC count, platelet count, and Sokal index were found to be statistically different in the two groups (Table 2).
Table 2. Characteristics of 56 Patients in Continuous CCR or Not
Because the cohort of patients who stopped therapy is small, it is difficult to determine the factors influencing relapse. However, it is interesting to notice the different characteristics for the subset of 15 patients (Table 3). Among the patients who did not experience relapse, all were females belonging to the low-risk group according to the Sokal index. Among the eight patients who did experience relapse, seven were males and two belonged to the low-risk group according to the Sokal index. All six patients with a CCR duration of less than 2 years (median, 9 months; range, 5 to 19 months) experienced relapse. In contrast, among the nine patients with a long period of CCR before cessation of treatment (median, 60 months; range, 24 to 84 months), only two experienced relapse (P < .0001) (Fig 6). One patient with a CCR of 35 months relapsed after a few months but still had a low percentage of Ph-positive cells 6 years after cessation of IFN without any treatment. The other remained in CCR for a long period after stopping IFN but later experienced relapse. This was the same patient who was in partial hematologic remission 95 months after having stopped IFN.
Table 3. Characteristics of Patients Who Did (lost CCR) and Did Not Experience Relapse Among Those Who Stopped IFN (n = 15)
Fig 6. Probability of remaining in CCR for the patients who were in CCR for at least 24 months (n = 7) compared with the other patients (n = 8) (P < .0001). —, CCR more than 24 months; ---, CCR less than 24 months.
DISCUSSION
IFN began to be used for the treatment of CML in the middle of the 1980s, and the follow-up for good responders is now substantial.19 It has become the treatment of choice for newly diagnosed patients in chronic-phase CML who are ineligible for allogeneic bone marrow transplantation because of their age or lack of a suitable donor. Several prospective randomized studies have shown that survival is prolonged in comparison with conventional chemotherapy.19 IFN can induce cytogenetic response, but a few patients sometimes remain in CCR for a long time. The finding of long-lasting cytogenetic remission in CML patients treated with IFN raises the question of whether this agent is actually able to cure the disease even in a minority of patients and when treatment should be stopped.
Therefore, we observed 15 patients in our center who stopped IFN while they were in CCR. Among these 15 patients, we decided to stop the treatment in six because a very low level of residual disease was obtained. This was defined at molecular level by PCR but with a rather insensitive technique. Indeed, the latter was able to discriminate only one leukemic cell among 104 normal cells. Because we started follow-up of the patients more than 10 years ago, we did not modify our technique so that one sample was really comparable with another. Following-up our patients by a more recent technique such as real-time PCR would obviously be more useful.
Among the patients belonging to the low-level residual group, none experienced relapse with a follow-up of 3 years. All of these patients were in CCR for at least 24 months before stopping treatment. Among the patients who stopped for toxic reasons, only one did not experience relapse, but he had a long CCR of more than 2 years before treatment was discontinued.
These results are similar to those reported by the M.D. Anderson Cancer Center in Houston, TX. They reported 18 patients among 28 who remained in CCR with a median duration of 3.5 years (range, 1 to 10 years) after discontinuing IFN.20 However, the criterion for stopping IFN in that study was a sustained CCR of more than 1 year's duration. Recently, Hochhaus et al21 reported five of six patients in stable remission having a very low minimum residual disease analyzed by quantitative PCR who had ceased IFN therapy with a median follow-up of 67 months (range, 26 to 114 months).
Discordant findings in the literature regarding molecular remissions are attributable to the sensitivity of the different PCR techniques. Strictly speaking, molecular remission does not really exist in CML, because BCR-ABL-positive cells (1/107) have been detected in a significant proportion of normal healthy adults.22,23 Therefore, molecular remission is not in itself evidence that IFN can cure CML.
If the level of residual disease reaches a plateau corresponding to the limit of the sensitivity of our technique, these particular patients do not relapse, at least to the best of our knowledge at the moment. Leukemic cells might in fact persist in these patients in CCR. Indeed, if a more sensitive technique were to be used, such as those described by other groups, PCR results would probably be positive. In addition, it has recently been reported that endothelial cells expressing the BCR-ABL gene could be found in the vascular endothelium of CML patients.24
This small group of patients illustrates the hypothesis that persistence of low numbers of Ph-positive cells does not necessarily imply hematologic relapse. In addition, one patient surprisingly remained with a low percentage of Ph-positive cells more than 6 years after stopping the treatment. As mentioned above, very few studies have precisely examined the follow-up of CCR patients after stopping IFN, and none of these studies has reported a case relapsing with a sustained low percentage of Ph-positive cells during follow-up after cessation. IFN has immune-modulatory effects that increase expression of HLA class I antigens on tumor cells, but there is no evidence that these play a role in CML. It has also been speculated that the anti-CML activity of IFN may be mediated through the activation of dendritic cells.25,26 In addition, one of the most frequent side effects of IFN is autoimmune disorders.27
Longer-term follow-up is needed to determine whether such patients are indeed cured of their CML. Inhibiting the activity of the BCR-ABL kinase with STI571 or imatinib mesylate represents a novel, highly selective approach to the therapy of CML, given the dominant role that BCR-ABL plays in the deregulated cell proliferation in this disease.13 In a phase I/II dose-escalation study, STI571 induced substantial hematologic and cytogenetic responses at daily doses of 300 mg and higher in patients with chronic-phase CML.14 If the cytogenetic responses are confirmed in the future, the issue of curtailing treatment might also become relevant in CCR patients after STI571.
Because the survival and the probability of relapse were not different in the group of patients who stopped IFN and the group who continued, it is indeed possible to stop IFN in CCR patients. It could be withdrawn after 2 years of a sustained CCR, because all patients with a CCR of less than 2 years experienced relapse. Quantification of BCR-ABL transcripts at the moment when IFN is stopped would be helpful to select suitable candidates in the future for prospective studies and to define a threshold value.
