Chronic Lymphocytic Leukemia Therapy Guided by Measurable Residual Disease.

BACKGROUND: The combination of ibrutinib and venetoclax has been shown to improve outcomes in patients with chronic lymphocytic leukemia (CLL) as compared with chemoimmunotherapy. Whether ibrutinib-venetoclax and personalization of treatment duration according to measurable residual disease (MRD) is more effective than fludarabine-cyclophosphamide-rituximab (FCR) is unclear. METHODS: In this phase 3, multicenter, randomized, controlled, open-label platform trial involving patients with untreated CLL, we compared ibrutinib-venetoclax and ibrutinib monotherapy with FCR. In the ibrutinib-venetoclax group, after 2 months of ibrutinib, venetoclax was added for up to 6 years of therapy. The duration of ibrutinib-venetoclax therapy was defined by MRD assessed in peripheral blood and bone marrow and was double the time taken to achieve undetectable MRD. The primary end point was progression-free survival in the ibrutinib-venetoclax group as compared with the FCR group, results that are reported here. Key secondary end points were overall survival, response, MRD, and safety. RESULTS: A total of 523 patients were randomly assigned to the ibrutinib-venetoclax group or the FCR group. At a median of 43.7 months, disease progression or death had occurred in 12 patients in the ibrutinib-venetoclax group and 75 patients in the FCR group (hazard ratio, 0.13; 95% confidence interval [CI], 0.07 to 0.24; P<0.001). Death occurred in 9 patients in the ibrutinib-venetoclax group and 25 patients in the FCR group (hazard ratio, 0.31; 95% CI, 0.15 to 0.67). At 3 years, 58.0% of the patients in the ibrutinib-venetoclax group had stopped therapy owing to undetectable MRD. After 5 years of ibrutinib-venetoclax therapy, 65.9% of the patients had undetectable MRD in the bone marrow and 92.7% had undetectable MRD in the peripheral blood. The risk of infection was similar in the ibrutinib-venetoclax group and the FCR group. The percentage of patients with cardiac serious adverse events was higher in the ibrutinib-venetoclax group than in the FCR group (10.7% vs. 0.4%). CONCLUSIONS: MRD-directed ibrutinib-venetoclax improved progression-free survival as compared with FCR, and results for overall survival also favored ibrutinib-venetoclax. (Funded by Cancer Research UK and others; FLAIR ISRCTN Registry number, ISRCTN01844152; EudraCT number, 2013-001944-76.).

Ibrutinib and rituximab versus fludarabine, cyclophosphamide, and rituximab for patients with previously untreated chronic lymphocytic leukaemia (FLAIR): interim analysis of a multicentre, open-label, randomised, phase 3 trial.

BACKGROUND: The approval of Bruton tyrosine kinase (BTK) inhibitors in patients with previously untreated chronic lymphocytic leukaemia (CLL) was based on trials which compared ibrutinib with alkylating agents in patients considered unfit for fludarabine, cyclophosphamide, and rituximab, the most effective chemoimmunotherapy in CLL. We aimed to assess whether ibrutinib and rituximab is superior to fludarabine, cyclophosphamide, and rituximab in terms of progression-free survival. METHODS: This study is an interim analysis of FLAIR, which is an open-label, randomised, controlled, phase 3 trial in patients with previously untreated CLL done at 101 UK National Health Service hospitals. Eligible patients were between 18 and 75 years of age with a WHO performance status of 2 or less and disease status requiring treatment according to International Workshop on CLL criteria. Patients with greater than 20% of their CLL cells having the chromosome 17p deletion were excluded. Patients were randomly assigned (1:1) by means of minimisation (Binet stage, age, sex, and centre) with a random element in a web-based system to ibrutinib and rituximab (ibrutinib administered orally at 420 mg/day for up to 6 years; rituximab administered intravenously at 375 mg/m2 on day 1 of cycle 1 and at 500 mg/m2 on day 1 of cycles 2-6 of a 28-day cycle) or fludarabine, cyclophosphamide, and rituximab (fludarabine 24 mg/m2 per day orally on day 1-5, cyclophosphamide 150 mg/m2 per day orally on days 1-5; rituximab as above for up to 6 cycles). The primary endpoint was progression-free survival, analysed by intention to treat. Safety analysis was per protocol. This study is registered with ISRCTN, ISRCTN01844152, and EudraCT, 2013-001944-76, and recruiting is complete. FINDINGS: Between Sept 19, 2014, and July 19, 2018, of 1924 patients assessed for eligibility, 771 were randomly assigned with median age 62 years (IQR 56-67), 565 (73%) were male, 206 (27%) were female and 507 (66%) had a WHO performance status of 0. 385 patients were assigned to fludarabine, cyclophosphamide, and rituximab and 386 patients to ibrutinib and rituximab. After a median follow-up of 53 months (IQR 41-61) and at prespecified interim analysis, median progression-free survival was not reached (NR) with ibrutinib and rituximab and was 67 months (95% CI 63-NR) with fludarabine, cyclophosphamide, and rituximab (hazard ratio 0·44 [95% CI 0·32-0·60]; p<0·0001). The most common grade 3 or 4 adverse event was leukopenia (203 [54%] patients in the fludarabine, cyclophosphamide, and rituximab group and 55 [14%] patients in the ibrutinib and rituximab group. Serious adverse events were reported in 205 (53%) of 384 patients receiving ibrutinib and rituximab compared with 203 (54%) of 378 patients receiving fludarabine, cyclophosphamide, and rituximab. Two deaths in the fludarabine, cyclophosphamide, and rituximab group and three deaths in the ibrutinib and rituximab group were deemed to be probably related to treatment. There were eight sudden unexplained or cardiac deaths in the ibrutinib and rituximab group and two in the fludarabine, cyclophosphamide, and rituximab group. INTERPRETATION: Front line treatment with ibrutinib and rituximab significantly improved progression-free survival compared with fludarabine, cyclophosphamide, and rituximab but did not improve overall survival. A small number of sudden unexplained or cardiac deaths in the ibrutinib and rituximab group were observed largely among patients with existing hypertension or history of cardiac disorder. FUNDING: Cancer Research UK and Janssen.

Obinutuzumab as consolidation after chemo-immunotherapy: Results of the UK National Cancer Research Institute phase II/III GALACTIC trial.

The GA101 (obinutuzumab) monocLonal Antibody as Consolidation Therapy In chronic lymphocytic leukaemia (CLL) (GALACTIC) was a seamless phase II/III trial designed to test whether consolidation with obinutuzumab is safe and eradicates minimal residual disease (MRD) and, subsequently, whether this leads to prolonged progression-free survival (PFS) in patients with CLL who have recently responded to chemo-immunotherapy. Patients with a response 3-24 months after chemotherapy were assessed for MRD. MRD-positive patients were randomised to receive consolidation therapy with obinutuzumab or no consolidation. The trial closed after the phase II part due to slow recruitment. In all, 48 patients enrolled of whom 19 were MRD negative and were monitored. Of the 29 MRD-positive patients, 14 were randomised to receive consolidation and 15 to no consolidation. At 6 months after randomisation, 10 and 13 consolidated patients achieved MRD negativity by flow cytometry (sensitivity 10-4 ) in bone marrow and peripheral blood respectively. PFS was significantly better in consolidated patients compared to non-consolidated patients (p = 0.001). No difference was observed in PFS, overall survival or duration of MRD negativity when comparing the 10 MRD-negative patients after consolidation with the 19 MRD-negative patients in the monitoring group. Common adverse events in the consolidation arm were thrombocytopenia, infection, and cough. Only 1% of events were infusion-related reactions. This observation provides further evidence that consolidation to achieve MRD negativity improves outcomes in CLL and that obinutuzumab is well tolerated in patients with low levels of disease.

A platform trial in practice: adding a new experimental research arm to the ongoing confirmatory FLAIR trial in chronic lymphocytic leukaemia.

BACKGROUND: The FLAIR trial in chronic lymphocytic leukaemia has a randomised, controlled, open-label, confirmatory, platform design. FLAIR was successfully amended to include an emerging promising experimental therapy to expedite its assessment, greatly reducing the time to reach the primary outcome compared to running a separate trial and without compromising the validity of the research or the ability to recruit to the trial and report the outcomes. The methodological and practical issues are presented, describing how they were addressed to ensure the amendment was a success. METHODS: FLAIR was designed as a two-arm trial requiring 754 patients. In stage 2, two new arms were added: a new experimental arm and a second control arm to protect the trial in case of a change in practice. In stage 3, the original experimental arm was closed as its planned recruitment target was reached. In total, 1516 participants will be randomised to the trial. RESULTS: The changes to the protocol and randomisation to add and stop arms were made seamlessly without pausing recruitment. The statistical considerations to ensure the results for the original and new hypotheses are unbiased were approved following peer review by oversight committees, Cancer Research UK, ethical and regulatory committees and pharmaceutical partners. These included the use of concurrent comparators in case of any stage effect, appropriate control of the type I error rate and consideration of analysis methods across trial stages. The operational aspects of successfully implementing the amendments are described, including gaining approvals and additional funding, data management requirements and implementation at centres. CONCLUSIONS: FLAIR is an exemplar of how an emerging experimental therapy can be assessed within an existing trial structure without compromising the conduct, reporting or validity of the trial. This strategy offered considerable resource savings and allowed the new experimental therapy to be assessed within a confirmatory trial in the UK years earlier than would have otherwise been possible. Despite the clear efficiencies, treatment arms are rarely added to ongoing trials in practice. This paper demonstrates how this strategy is acceptable, feasible and beneficial to patients and the wider research community. TRIAL REGISTRATION: ISRCTN Registry ISRCTN01844152 . Registered on August 08, 2014.

Clinical significance of DNA methylation in chronic lymphocytic leukemia patients: results from 3 UK clinical trials.

Chronic lymphocytic leukemia patients with mutated immunoglobulin heavy-chain genes (IGHV-M), particularly those lacking poor-risk genomic lesions, often respond well to chemoimmunotherapy (CIT). DNA methylation profiling can subdivide early-stage patients into naive B-cell-like CLL (n-CLL), memory B-cell-like CLL (m-CLL), and intermediate CLL (i-CLL), with differing times to first treatment and overall survival. However, whether DNA methylation can identify patients destined to respond favorably to CIT has not been ascertained. We classified treatment-naive patients (n = 605) from 3 UK chemo and CIT clinical trials into the 3 epigenetic subgroups, using pyrosequencing and microarray analysis, and performed expansive survival analysis. The n-CLL, i-CLL, and m-CLL signatures were found in 80% (n = 245/305), 17% (53/305), and 2% (7/305) of IGHV-unmutated (IGHV-U) cases, respectively, and in 9%, (19/216), 50% (108/216), and 41% (89/216) of IGHV-M cases, respectively. Multivariate Cox proportional analysis identified m-CLL as an independent prognostic factor for overall survival (hazard ratio [HR], 0.46; 95% confidence interval [CI], 0.24-0.87; P = .018) in CLL4, and for progression-free survival (HR, 0.25; 95% CI, 0.10-0.57; P = .002) in ARCTIC and ADMIRE patients. The analysis of epigenetic subgroups in patients entered into 3 first-line UK CLL trials identifies m-CLL as an independent marker of prolonged survival and may aid in the identification of patients destined to demonstrate prolonged survival after CIT.

An increased fraction of circulating miR-363 and miR-16 is particle bound in patients with chronic lymphocytic leukaemia as compared to normal subjects.

OBJECTIVES: In vitro culture studies have shown that miR-363 is enriched in extracellular vesicles from chronic lymphocytic leukaemia cells. We wondered whether miR-363 was detectable in plasma, which is an essential precondition for further studies to assess its usefulness as a biomarker. Using samples from two clinical trials: one enrolling patients with advanced disease and the other asymptomatic patients with early stage disease, we determined plasma miR-363 levels and secondly investigated the distribution of this miRNA between plasma and particle bound fractions in patients and normal subjects. RESULTS: Advanced disease (n = 95) was associated with higher levels of miR-363 than early stage disease (n = 45) or normal subjects (n = 11) but there was no association with markers of prognosis. The distribution of specific miRNA between particle bound and plasma protein fractions was investigated using size exclusion chromatography on plasma from patients (n = 4) and normal subjects (n = 3). ~ 20% of total miR-16 and miR-363 is particle bound in patients while there was no detectable particle bound material in normal subjects. Our work demonstrates that miR-363 levels are raised in chronic lymphocytic leukaemia patients and raises the possibility that distribution of circulating miRNA between plasma fractions differs in health and disease.

Recommendations on multiple testing adjustment in multi-arm trials with a shared control group.

Multi-arm clinical trials assessing multiple experimental treatments against a shared control group can offer efficiency advantages over independent trials through assessing an increased number of hypotheses. Published opinion is divided on the requirement for multiple testing adjustment to control the family-wise type-I error rate (FWER). The probability of a false positive error in multi-arm trials compared to equivalent independent trials is affected by the correlation between comparisons due to sharing control data. We demonstrate that this correlation in fact leads to a reduction in the FWER, therefore FWER adjustment is not recommended solely due to sharing control data. In contrast, the correlation increases the probability of multiple false positive outcomes across the hypotheses, although standard FWER adjustment methods do not control for this. A stringent critical value adjustment is proposed to maintain equivalent evidence of superiority in two correlated comparisons to that obtained within independent trials. FWER adjustment is only required if there is an increased chance of making a single claim of effectiveness by testing multiple hypotheses, not due to sharing control data. For competing experimental therapies, the correlation between comparisons can be advantageous as it eliminates bias due to the experimental therapies being compared to different control populations.

Assessment of ibrutinib plus rituximab in front-line CLL (FLAIR trial): study protocol for a phase III randomised controlled trial.

BACKGROUND: Treatment of chronic lymphocytic leukaemia (CLL) has seen a substantial improvement over the last few years. Combination immunochemotherapy, such as fludarabine, cyclophosphamide and rituximab (FCR), is now standard first-line therapy. However, the majority of patients relapse and require further therapy, and so new, effective, targeted therapies that improve remission rates, reduce relapses, and have fewer side effects, are required. The FLAIR trial will assess whether ibrutinib plus rituximab (IR) is superior to FCR in terms of progression-free survival (PFS). METHODS/DESIGN: FLAIR is a phase III, multicentre, randomised, controlled, open, parallel-group trial in patients with previously untreated CLL. A total of 754 participants will be randomised on a 1:1 basis to receive standard therapy with FCR or IR. Participants randomised to FCR will receive a maximum of six 28-day treatment cycles. Participants randomised to IR will receive six 28-day cycles of rituximab, and ibrutinib taken daily for 6 years until minimal residual disease (MRD) negativity has been recorded for the same amount of time as it took to become MRD negative, or until disease progression. The primary endpoint is PFS according to the International Workshop on CLL (IWCLL) criteria. Secondary endpoints include: overall survival; proportion of participants with undetectable MRD; response to therapy by IWCLL criteria; safety and toxicity; health-related quality of life (QoL); and cost-effectiveness. DISCUSSION: The trial aims to provide evidence for the future first-line treatment of CLL patients by assessing whether IR is superior to FCR in terms of PFS, and whether toxicity rates are favourable. TRIAL REGISTRATION: ISRCTN01844152 . Registered on 8 August 2014, EudraCT number 2013-001944-76 . Registered on 26 April 2013.

GA101 (obinutuzumab) monocLonal Antibody as Consolidation Therapy In CLL (GALACTIC) trial: study protocol for a phase II/III randomised controlled trial.

BACKGROUND: Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia. Achieving minimal residual disease (MRD) negativity in CLL is an independent predictor of survival even with a variety of different treatment approaches and regardless of the line of therapy. METHODS/DESIGN: GA101 (obinutuzumab) monocLonal Antibody as Consolidation Therapy In CLL (GALACTIC) is a seamless phase II/III, multi-centre, randomised, controlled, open, parallel-group trial for patients with CLL who have recently responded to chemotherapy. Participants will be randomised to receive either obinutuzumab (GA-101) consolidation or no treatment (as is standard). The phase II trial will assess safety and short-term efficacy in order to advise on continuation to a phase III trial. The primary objective for phase III is to assess the effect of consolidation therapy on progression-free survival (PFS). One hundred eighty-eight participants are planned to be recruited from forty research centres in the United Kingdom. DISCUSSION: There is evidence that achieving MRD eradication with alemtuzumab consolidation is associated with improvements in survival and time to progression. This trial will assess whether obinutuzumab is safe in a consolidation setting and effective at eradicating MRD and improving PFS. TRIAL REGISTRATION: ISRCTN, 64035629 . Registered on 12 January 2015. EudraCT, 2014-000880-42 . Registered on 12 November 2014.

Clinical effectiveness and cost-effectiveness results from the randomised, Phase IIB trial in previously untreated patients with chronic lymphocytic leukaemia to compare fludarabine, cyclophosphamide and rituximab with fludarabine, cyclophosphamide, mitoxantrone and low-dose rituximab: the Attenuated dose Rituximab with ChemoTherapy In Chronic lymphocytic leukaemia (ARCTIC) trial.

BACKGROUND: The conventional frontline therapy for fit patients with chronic lymphocytic leukaemia (CLL) is fludarabine, cyclophosphamide and rituximab (FCR). Rituximab (Mabthera®, Roche Products Ltd) targets the CD20 antigen, which is expressed at low levels in CLL. The standard dose of rituximab in CLL (375 mg/m2 in cycle 1 and 500 mg/m2 in cycles 2-6) was selected based on toxicity data only. Small doses of rituximab (as low as 20 mg) have biological activity in CLL, with an immediate reduction in circulating CLL cells and down-regulation of CD20. Phase II trials had suggested improved efficacy with the addition of mitoxantrone to FCR. The key assumption for the Attenuated dose Rituximab with ChemoTherapy In CLL (ARCTIC) trial was that the addition of mitoxantrone to fludarabine, cyclophosphamide and low-dose rituximab would be more effective than conventional FCR. OBJECTIVES: To assess whether fludarabine, cyclophosphamide, mitoxantrone and low-dose rituximab (FCM-miniR) (100 mg of rituximab per cycle) was non-inferior to FCR in frontline CLL. Complete response (CR) rate was the primary end point, with the secondary end points being progression-free survival (PFS), overall survival (OS), overall response rate, eradication of minimal residual disease (MRD), safety and cost-effectiveness. DESIGN: ARCTIC was a UK multicentre, randomised, controlled, open, Phase IIB non-inferiority trial in previously untreated CLL. A total of 206 patients with previously untreated CLL who required treatment, according to the International Workshop on Chronic Lymphocytic Leukaemia criteria, were to be randomised to FCR or FCM-miniR. There was an independent Data Monitoring and Ethics Committee (DMEC) with a pre-planned interim efficacy assessment on 103 participants. RESULTS: The DMEC's interim analysis led to early trial closure. Although the response rates in both arms were higher than anticipated, FCM-miniR had a lower CR rate than FCR. This was partly attributable to the higher toxicity associated with mitoxantrone. A total of 100 participants completed FCR, 79 completed FCM-miniR and 21 commenced FCM-miniR but switched to FCR following DMEC recommendations. The CR rate for participants receiving FCR was 76%, compared with 55% for FCM-miniR (adjusted odds ratio 0.37; 95% confidence interval 0.19 to 0.73). Key secondary end points also showed that FCR was superior, with more participants achieving MRD negativity (57% for FCR vs. 46% for FCM-miniR). More participants experienced a serious adverse reaction with FCM-miniR compared with FCR (50% vs. 41%). At a median of 37.3 months' follow-up, the PFS and OS rates are good compared with previous studies, with no significant difference between the treatment arms. The economic analysis indicates that because FCM-miniR is less effective than FCR, FCM-miniR is not expected to be cost-effective over a lifetime horizon, producing a mean cost-saving of -£7723, a quality-adjusted life-year loss of -0.73 and a resulting incremental net monetary loss of -£6780. CONCLUSIONS: FCM-miniR is less well tolerated, with poorer response rates, than FCR, partly owing to the additional toxicity associated with mitoxantrone. In view of this, FCM-miniR will not be taken forward into a larger definitive Phase III trial. The trial demonstrated that oral FCR yields extremely high response rates compared with historical series with intravenous chemotherapy. FUTURE WORK: We shall compare the results of ARCTIC with those of the ADMIRE (Does the ADdition of Mitoxantrone Improve Response to FCR chemotherapy in patients with CLL?) trial, which compared FCR with FCM-R to assess the efficacy of low- versus standard-dose rituximab, allowing for the toxicity associated with mitoxantrone. TRIAL REGISTRATION: Current Controlled Trials ISRCTN16544962. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 21, No. 28. See the NIHR Journals Library website for further project information.

Eradication of minimal residual disease improves overall and progression-free survival in patients with chronic lymphocytic leukaemia, evidence from NCRN CLL207: a phase II trial assessing alemtuzumab consolidation.

With immunochemotherapy, remission duration and survival in patients with chronic lymphocytic leukaemia is dependent on the level of minimal residual disease (MRD) after treatment. This phase II trial assessed alemtuzumab consolidation post-chemotherapy in patients who responded with persistent low levels of detectable disease. Blood was screened for MRD using multi-parameter flow cytometry, 6-24 months post-chemotherapy. MRD-positive participants received alemtuzumab 30 mg subcutaneously 3 times weekly for 6 weeks. Following a marrow assessment, MRD-negative participants or non-responders stopped therapy and MRD-positive participants with 1 + log reduction had 6 more weeks of alemtuzumab. Alemtuzumab consolidation was received by 47 participants. One death and 19 of 22 serious adverse events reported from 17 (36%) participants were alemtuzumab-related. MRD eradication from blood and bone marrow was achieved in 39 (83%) participants at the end of consolidation, with 18 (38%) remaining MRD-negative in the blood 6 months later. Of the 18 participants who were MRD-negative at 6 months, the median time to MRD relapse was 46 months, which was similar to patients who were MRD-negative at baseline and were followed up. The 5-year progression-free survival (PFS) and overall survival (OS) of participants who were MRD-negative at 6 months was significantly better than MRD-positive participants [PFS: 78% vs. 39% (P = 0·010), OS: 89% vs. 64% (P = 0·029)].

Chemotherapy plus Ofatumumab at Standard or Mega dose in relapsed CLL (COSMIC) trial: study protocol for a phase II randomised controlled trial.

BACKGROUND: Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia. Combination immunochemotherapy such as fludarabine, cyclophosphamide and rituximab is the standard first line therapy in fit patients, but there is limited evidence regarding the optimal treatment of patients after relapse. Ofatumumab as monotherapy has been proven to be effective in the treatment of relapsed, refractory CLL, and as it is not myelotoxic, it is an ideal drug to combine with chemotherapy. However, the optimal dose of ofatumumab in this setting is not known. The Chemotherapy plus Ofatumumab at Standard or Mega dose in relapsed CLL (COSMIC) trial will assess the efficacy and safety of standard and high (mega) doses of ofatumumab combined with bendamustine or a combination of fludarabine and cyclophosphamide to determine which, if either, schedule should progress to a phase III trial. METHODS/DESIGN: COSMIC is a phase II, multi-centre, randomised, open, parallel group trial for patients with relapsed CLL who are not refractory to fludarabine-based chemotherapy. Participants will be randomised to receive either standard dose or mega dose ofatumumab. Both doses will be given in combination with either bendamustine or fludarabine and cyclophosphamide chemotherapy backbone. The primary objective is to assess the proportion of participants achieving a complete remission following therapy with the two treatment arms (mega versus standard), as assessed at 3 months post treatment. The treatment groups will be assessed independently to determine whether the level of response is acceptable in relation to pre-specified criteria. If both treatment groups show an acceptable level of response, selection criteria will be used to determine which to take forward to a confirmatory phase III trial. A key secondary objective is to assess the dynamics of minimal residual disease (MRD) levels in relapsed disease. Eighty-two participants are planned to be recruited from 18 research centres in the UK. DISCUSSION: Currently there is limited evidence regarding the optimal treatment of patients with relapsed or refractory CLL, and so suitable therapies are urgently needed. The COSMIC trial will identify whether ofatumumab given in combination with chemotherapy is safe and effective in this population, and will identify the optimal doses for further investigation. TRIAL REGISTRATION: ISRCTN51382468 . Registered on 21 September 2011.

Characterizing and quantifying the effects of breast cancer therapy using mathematical modeling.

We designed a mathematical model to describe and quantify the mechanisms and dynamics of tumor growth, cell-kill and resistance as they affect durations of benefit after cancer treatment. Our aim was to explore how treatment efficacy may be related to primary tumor characteristics, with the potential to guide future trial design and appropriate selection of therapy. Assuming a log-normal distribution of both resistant disease and tumor doubling times generates disease-free survival (DFS) or invasive DFS curves with specific shapes. Using a multivariate mathematical model, both treatment and tumor characteristics are related to quantified resistant disease and tumor regrowth rates by allowing different mean values for the influence of different treatments or clinical subtypes on these two log-normal distributions. Application of the model to the CALGB 9741 adjuvant breast cancer trial showed that dose-dense therapy was estimated to achieve an extra 3/4 log of cell-kill compared to standard therapy, but only in patients with more rapidly growing ER-negative tumors. Application of the model to the AZURE trial of adjuvant bisphosphonate treatment suggested that the 5-year duration of zoledronic acid was adequate for ER-negative tumors, but may not be so for ER-positive cases, with increased recurrences after ceasing the intervention. Mathematical models can identify different effects of treatment by subgroup and may aid in treatment design, trial analysis, and appropriate selection of therapy. They may provide a more appropriate and insightful tool than the conventional Cox model for the statistical analysis of response durations.