Summary of main results
In this review, we addressed four different issues.
1) Is MX therapy effective in reducing the progression of disability and the frequency of clinical attacks?
Our data confirmed the clinical efficacy of MX on disease progression and relapse frequency in patients affected by MS. Most of the outcomes, either clinical or MRI-related, supported an efficacy of MX.
Regarding the proportion of participants with confirmed progression of disability, due to the different definition of disability progression across studies we decided to perform post hoc analyses additional to the originally planned primary outcome measure. The OR of MX-treated participants versus placebo-treated participants at one year was 0.24 (95% CI 0.04 to 1.33) using the three or six month confirmed definition. As regards the two year follow-up, the OR was 0.30 (95% CI 0.09 to 0.99) using the six month confirmed definition (one study, 58% of the participants) . While admitting that post hoc analysis, which included a less stringent definition of disability progression, may raise methodological issues, it is worthwhile to mention that the difference in the proportion of patients who experienced disability progression across the two treatment arms was similar and was confirmed by using any of these definitions. Moreover, it is still questionable whether to use the three or six month interval of confirmation of disability progression, even across Cochrane reviews (in Rice 2001: "disability progression is a sustained (3 or 6 months) increase in EDSS of at least 1 point recorded out of exacerbation"; in La Mantia 2010: "progression has been defined as a persistent worsening of at least 1 point in EDSS, recorded out of relapse and confirmed by a follow-up assessment at 6 months"), and we need to be more cautious when aggregating data on unconfirmed disability progression. The use of an interval of three or six months for a confirmation of disability progression does not substantially change the results of the Hartung study (Table 3, page 2022) as the numbers of progressed patients in the MX-and placebo-treated arms were 5/60 versus 14/64 using the three month interval and 4/60 versus 12/64 using the six month interval.
We also performed sensitivity analyses to consider the few patients who dropped out from the studies. In Hartung 2002, it was mentioned that analyses were performed according to an ITT principle (page 2022, second column, line 34). However, four patients (one placebo-treated and three MX-treated) dropped out before receiving any treatment were not included in the ITT analysis, and were therefore considered for the sensitivity analyses. The sensitivity analysis influenced the results at the one year but not at the two year follow-up.
As a general comment, we have also to consider that the EDSS scale is still the most widely used scale to assess disability progression in MS. It has many drawbacks, represented by its poor sensitivity to changes and moderate inter- and intra-observer reliability (Goodkin 1992). The efficacy of MX in reducing the progression of disability was less evident when the outcome was the difference in EDSS score at the end versus the beginning of treatment, even if a single study was used for the analysis.
MX was effective in reducing the relapse rate (measured as the annualised relapse rate) and in increasing the proportion of patients free from relapses; the efficacy was not modified by the assignment of dropped out patients. From available data, however, it is not possible to ascertain whether the efficacy of MX in reducing the progression of disability is due to a reduction in the frequency of clinical relapses or to other reasons. The clinical efficacy of MX was paralleled by that on MRI-derived outcome measures. When considering MRI measures of inflammatory activity, such as the number of active lesions and the proportion of patients with active lesions (defined as enhancing-lesions on T1 scans), a statistically significant MX efficacy was found for the latter but not for the former measure. On the contrary, it was not possible to explore and aggregate MRI measures of 'neurodegeneration', such as the measurement of brain atrophy, as no data were available from the selected studies.
Admittedly, as a limitation of our meta-analysis, there were many sources of potential heterogeneity across the different trials represented by the following.
a) The types of enrolled patients: in Edan 1997, SP with worsening disability (progression of at least 2 points on EDSS scale in the previous year) and worsening RR (two relapses with sequelae in the previous year) with evidence of MRI inflammatory activity; in Millefiorini 1997, RR with at least two relapses in the previous two years; and in Hartung 2002, SP, PR and worsening RR with evidence of a progression of at least 1 point of EDSS respectively in the preceding 18 and 12 months.
b) The frequency, interval of administration and total dosage of the drug: 6 monthly cycles of 20 mg combined with 1 g of methylprednisolone in Edan 1997; 12 monthly pulses of 8 mg/m2 of body surface in Millefiorini 1997; 8 pulses every 3 months of 12 mg/m2 of body surface in Hartung 2002.
c) The addition of steroids to the placebo and active arm in Edan 1997.
However, no major heterogeneity was found according to the statistical methods used, which were planned in the original protocol, in any of the explored outcome measures. This possibly suggests that, at least in the short-term period, none of the above variables acted as effect modifiers or confounders of drug efficacy. We could also argue that the test used (Cochran's Q) is poor in sensitivity when detecting true heterogeneity among studies as being significant, especially when few studies are included in the meta-analysis.
Another limitation was the lack of a uniform definition of some of the explored outcome measures across the different studies, especially as regards the definition of confirmed progression of disability for which a correct time interval of six months was defined only by Hartung 2002. It is highly warranted to use the same definition of outcome measures across different trials in order to make data from different trials most comparable and available for pooling. Moreover, no data were available from longer follow-up studies that were able to provide information on long-term drug effectiveness. There are some data on MX efficacy at three year follow-up, one year after the end of the trial, in a subgroup of patients from Hartung 2002. Six out of 42 (16%) MX-treated participants and 16/40 (42%) placebo-treated participants showed a confirmed progression of disease leading to an OR of 0.25 (95% CI 0.09 to 0.73; P = 0.01). However, these analyses were not performed according to an ITT analysis and, therefore, they have limited clinical relevance.
2) Which patients should get MX?
As previously reported, the selected participants were different across studies, even though no major heterogeneity has been found according to the statistical methods used. It is, however, impossible to establish whether small differences between trials were due to the selected patients or to the different treatment regimens. Gonsette recently suggested that MX should only be used in patients with worsening RR, defined as "RR patients experiencing frequent and disabling relapses likely leading to permanent severe disability", and an SP course with evidence of worsening disability, defined as an increase of at least 1 EDSS point per year (Gonsette 2003).
3) What should be the dosage and frequency of administration of MX?
No clear indications can be derived from this meta-analysis. A recent review (Gonsette 2003) suggests a treatment regimen with an induction phase (12 mg/m2 every month for 3 months) followed by a maintenance phase (12 mg/m2 every 3 months for 21 months), which seems to be an acceptable trade-off to maintain treatment for 2 years with a reasonable cumulative dose (120 mg/ m2). This scheme is supported by the in vivo effect of MX administration on immune cells, which is characterized by a marked immunosuppression (namely, leukopenia < 2000/mm3 or lymphopenia < 1000/mm3) after three to four monthly infusions maintained for two years with a subsequent trimonthly administration. The dosage needs to be adjusted according to the haematological profiles shown before the next treatment, as reported in Table 2. It is advisable to adjust the dosage regimen rather than to delay infusions. The treatment regimen suggested by Gonsette 2003 is very similar to that reported in Hartung 2002, which represents the largest trial.
However, it is worthwhile mentioning that another retrospective open-label study (Debouverie 2004) confirmed the effectiveness of the treatment regimen recommended in Edan 1997 of six monthly cycles of 20 mg of MX combined with steroids across worsening RR and SP MS patients. One year after the end of treatment, 44% of the patients had an EDSS improvement, 39% remained stable and 17% had deteriorated.
Table 2. Mitoxantrone dosage adjustment
|Dose to be given||100%||90%||75%||Stop|
|If: Leucocytes (x1000/ml)||>= 4||3-3.99||2-2.99||< 2|
|If: Granulocytes (x1000/ml)||>= 2||1.5-1.99||1-1.49||< 1|
|If: Platelets (x1000/ml)||>= 100||75-99||50-74||< 50|
More recent studies are suggesting the use of this drug as a short-term induction treatment followed by maintenance immunomodulant treatment in aggressive forms of MS (Edan 2011).
4) Is MX a safe drug?
According to the conclusions of the FDA safety review, "MX was well tolerated with no deaths, few serious adverse events and few discontinuations of therapy. No previously unrecognised toxicities were observed in these studies. No serious cardiotoxicity events were observed although these studies did not expose patients to cumulative doses above 100 mg/m2. Cardiotoxicity, neutropenia and its sequelae, amenorrhoea, which in some cases may be permanent, and the potential for late occurring leukaemia are the major safety concerns associated with MX use (page 42)". Our meta-analysis confirmed that there were no deaths or symptomatic cardiac events among MX-treated patients. Seven out of 111 (6.3% of the total) MX-treated participants interrupted the treatment for major side effects, of whom one had asymptomatic LVEF lower than 50%, one suffered a major depressive episode, one had repeated episodes of nausea and vomiting, one had repeated urinary infections and one had renal failure. Considering the two out of 110 (2% of the total) placebo participants who had treatment interrupted, one was due to hepatitis and one had a myocardial infarction.
Thirty-five per cent of female MX-treated participants developed amenorrhoea, and almost 15% or 12% ??developed a persistent amenorrhoea which was still present at the end of the study. These data are similar to those reported by Edan et al, who followed up a cohort of 800 MX-treated MS participants and found that 6.7% of women younger than 35 years who received MX at a cumulative dose of 79 mg/m2 developed secondary amenorrhoea (Edan 2001 b). In these cases, a hormonal substitution therapy should be started at the onset of amenorrhoea. As a consequence, patients, especially if of child-bearing age, should be advised of this potential side effect and also on the potential but not fully established teratogenic effects of the drug.
Nausea and vomiting, alopecia and urinary tract infections were more frequent among MX-treated versus placebo-treated participants. There are reports of therapy-related acute leukaemia (TRAL) in MX-treated MS patients, possibly due to a real increment in frequency or to improved surveillance. In contrast to leukaemias associated with alkylating substances such as cyclophosphamide, MX-related acute leukaemias are characterized by a short latency, acute onset and cytogenetic changes similar to de novo leukaemias, such as translocations 11q23, 21q22 or inversion of chromosome 16.Most importantly, they usually respond to therapy (Quesnel 1993). In June 2004, a total of nine MX-treated MS patients, four of whom were single case reports, developed TRAL (Brassat 2002; Cattaneo 2003; Delisse 2004; Ghalie 2002a; Goodkin 2003; Heesen 2003; Radu 2002; Voltz 2004). As schematically reported by Voltz (Voltz 2004; page 473, Table 1), the onset of leukaemia ranged from three months after the end of MX treatment (Goodkin 2003) to five years (Vicari 1998) across MX-treated MS patients who developed leukaemia, but it mostly occurred within two years following the cessation of treatment. The cumulative dose of MX treatment before the onset of leukaemia ranged from 48 mg/m2 to 120 mg/m2. All of the cases underwent chemotherapy, which was successful in seven out of nine patients but two patients died. There is a recent report of a case of acute promyelocytic leukaemia in a patient who received only 15 mg of MX; however, this patient was affected by breast cancer and, before receiving MX, she had also been treated with radiotherapy (Mistry 2005). A meta-analysis tried to measure the incidence of leukaemia among a cohort of 1378 MX-treated MS participants from three different trials (Ghalie 2002a): the MIMS study (Hartung 2002), a French retrospective study (Edan 2001), and a German retrospective study (Mauch 1999). An incidence proportion of 0.15% was found after a mean follow-up of 36 months in 1378 patients. This is higher than the proportion of de novo leukaemias in healthy patients, which typically ranges from 0.001% at 20 years of age to 0.03% at 70 years of age, but lower than that among patients who underwent combined chemotherapy, including MX, for whom the leukaemia incidence proportion ranges from 2% to 12% (Felix 1998). A similar cumulative incidence, 0.21%, was reported by Voltz (Voltz 2004) by pooling the different cases of leukaemia reported in the literature. A registry to evaluate the long-term safety profile of MX has been developed (Goodkin 2001). In the following years, many case series and case reports have identified 56 to 57 cases of TRAL in MX-treated patients (for a summary, see table 2 in Marriott 2010), increasing the incidence of TRAL in MS patients to 33/4076, corresponding to an incidence of 0.81% and a number needed to harm (NNH) for TRAL development of 123. Most of these cases occurred within a few years of MX treatment. A recent multicentre retrospective cohort study on 3220 MS patients from 40 Italian MS Centers (Martinelli 2011) with a mean follow-up of 49 months revealed 30 cases of acute myelocytic leukaemia (AML), leading to a very similar incidence rate of 0.93% (95% CI 0.60% to -1.26%) and a mortality rate associated with AML of 37%. The median interval from drug start to AML diagnosis was 33 months, ranging from 13 to 84 months. A dose-dependent relationship was revealed by this study, corresponding to a 3% increase in the risk of AML for every one unit increase in MX cumulative dose. According to this analysis, a cumulative dose between 30 and 60 mg/m2 of body surface was suggested.
Given this evidence, it is particularly important to carefully check leukocytes blood levels before any additional MX cycle. A useful therapeutic scheme is reported in Table 2, where the dosage of the following MX cycle needs to be adjusted according to the haematological profile. Moreover, MX-treated patients should be followed up with complete blood cell counts; the optimal timing of such monitoring being unclear (Marriott 2010).
Cardiotoxicity is the major limiting factor in the long-term administration of MX and sets the maximum cumulative dose at a total of 140 mg/m2 body surface. MX cardiotoxicity appears to be due to the generation of free radicals by the drug which, according to human autopsy tissue concentration measures, are stored in elevated concentrations in the heart. The heart represents the third highest storage deposit of MX after the thyroid and liver (Stewart 1986). Benjamin 1985 examined endomyocardial biopsy specimens from 37 MX-treated patients, of whom six were treated with more than 100 mg/m2. Three of them had normal biopsies while the remaining 34 had histological changes resembling those caused by anthracyclines, namely a dilatation of the sarcoplasmic reticulum and myofibrillar dropout. This was, however, defined as minor and was not expected to be of clinical significance in the absence of other cardiac abnormalities. The potential risk of cardiotoxicity could be increased by the fact that a significant proportion of MS patients tend to have impaired cardiac function. Using radionuclide angiocardiography, Olindo 2002 found in a cohort of 40 MS patients that 25% of them had abnormal LVEFs.
A review (Ghalie 2002b) explored the occurrence of cardiotoxicity in 1378 MS patients enrolled in three different studies and who received a mean cumulative dose of MX of 60.5 mg/m2 and were followed-up for a mean of 30 months. Two cases of congestive heart failure (CHF) were reported, one had received a dose of MX higher than 140 mg/m2, leading to an incidence lower than 0.2%. Moreover, a 2.18% (95% CI 1.28 to 3.47) incidence of an LVEF decrease to below 50% was found among MX-treated patients. The probability of the event was weakly associated with the total cumulative dosage received (5% in patients treated with a total cumulative dosage of MX greater than 100 mg/m2 versus 1.8% in patients treated with a total cumulative dosage lower than 100 mg/m2), which suggests the importance of treating patients with lower dosages than 100 mg/m2 as well as monitoring them. This was previously described by De Castro 1995, who found that a total dose of MX of 96 mg/m2 was not associated with any cardiac toxicity in MS patients. A recent paper reported a significant decline of LVEF among 5/28 (17.8%) MS patients after three doses of MX and underpins the importance of monitoring these patients carefully (Avasarala 2003).
More recent studies have reported the occurrence of cardiotoxicity in MX-treated patients (for a summary, see table 1 in Marriott 2010) leading to an incidence rate of 12% (83/716) for decreased LVEF and of 0.4% (3/716) for congestive heart failure (CHF), corresponding to an NNH of 8 and 250 respectively. A phase IV clinical study of MX to assess its long-term safety and tolerability reported a 2% CHF occurrence in January 2008 (Rivera 2008). A registry has been established (Goodkin 2001) to evaluate MX long-term cardiotoxicity.
From a practical point of view, cardiotoxicity can be reduced by performing an electrocardiogram and echocardiography (echocardiogram, multi-gated cardiac scan (MUGA), MRI etc.) in all patients before initiation of therapy, and by performing an echocardiography every year during therapy and yearly after cessation of therapy (FDA 1999; FDA 2012; FDA 2012b). However, the recent report of the occurrence of delayed cardiotoxicity 24, 39 and 80 months after the last dose in three MS patients treated with a cumulative dose of 144 mg/m2 of MX underpins the need to extend the long-term surveillance of MX cardiotoxicity (Goffette 2005). Moreover, an echocardiography should be performed whenever patients develop symptoms of CHF. Treatment should never be started if the baseline LVEF is below 50% and should be stopped if the LVEF decreases by more than 10% from the baseline value or to below 50% during therapy. The total cumulative dosage of MX should not be higher than 100 mg/m2. It seems important to also reduce the rate of infusion over 30 minutes in order to decrease peak drug levels, which could be associated with a higher risk of cardiotoxicity (Gonsette 2003). A study (Bernitsas 2006) tested the potential reduction of MX-related cardiotoxicity by the concomitant administration of dexrazoxane (DRX). This drug protects the heart by chelating iron from complexes of iron and anthracyclines and reducing free radical formation (Mikol 2001; Weiss 1999). It could be administered to patients at the beginning of MX therapy. MS patients treated with (n = 28) or without DRX in conjunction with MX had significant LEVF reduction at one year, however the reduction was proportionally different (-3.8% compared to -8.6%, P < 0.001) (Bernitsas 2006).
We are aware of the development of a new analogue of MX, named BBR2778 or pixantrone (PIX), which belongs to a novel class of anthracene-9,10 diones characterized by the introduction of a nitrogen functionality in the nucleus and by the lack of two hydroxy groups. This could be an effective treatment for MS and not cardiotoxic (Krapcho 1994). According to experimental studies on EAE animal models, PIX was found to reduce the severity of the disease and, unlike MX, not to be cardiotoxic (Cavaletti 2004). Moreover, the weak cardiotoxicity of PIX has been confirmed in three phase II trials in PIX-treated patients affected with different tumours. We do not have more recent information on this drug.
Overall completeness and applicability of evidence
Despite the several sources of potential heterogeneity across the included trials, in terms of outcome measures definition (disability progression), inclusion criteria, and treatment dosage and regimen, they support and confirm the short-term efficacy and safety of the drug.
Quality of the evidence
Three trials involving 221 participants provided moderate evidence on the efficacy and short-term safety of the drug but no information on longer follow-up. Overall, their methodological quality was considered to be good with regard to the most common and relevant biases, even if type of issues found was heterogeneous
Potential biases in the review process
A careful and comprehensive search was performed to limit bias in the review process, which was not language restricted and was expanded to other sources, such as contacts with authors of the primary articles. The evaluation of eligibility of studies for inclusion in this review and the extraction of data were performed independently in order to minimise the additional potential biases to those already reported in the risk of bias table (Characteristics of included studies). Any disagreement was resolved by discussion between authors. Only three randomised, double-blinded controlled trials comparing MX administration versus placebo have been retrieved from the literature.
Agreements and disagreements with other studies or reviews
Our review is in substantial agreement with the more recent version of the report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology (Marriott 2010), which supports the efficacy of MX but also strengthens the long-term risk of cardiotoxicity and TRAL related to this drug, found in long-term observational studies.