40% of Females with Mantle Cell Lymphoma Are Managed with Initial Observation: Results from the MCL Biobank Observational Study

Background:

Although typically an aggressive disease some patients with Mantle Cell Lymphoma (MCL) follow an indolent course and may not benefit from immediate therapy. Several studies evaluating watch-and-wait (W&W) strategies in MCL show no detriment to patient survival and international guidelines acknowledge the strategy's suitability for a minority of patients. Differences in pathogenetic mechanisms have provided insight into variable clinical behaviour, but there is little clinical evidence to inform patient suitability for W&W.

The MCL Biobank Observational Study is a prospective study designed to distinguish indolent from aggressive forms of MCL. Tissue samples and baseline characteristics are collected at enrolment. The study has recruited over 550 patients across the UK and remains open to recruitment.

Method:

This analysis includes 315 patients from 58 centers in the United Kingdom enrolled between January 2015 and March 2018. All new MCL diagnoses compatible with WHO diagnostic criteria were eligible. Patients were enrolled within 90 days of diagnosis and prior to receiving therapy. Baseline data was recorded including investigator decision to start systemic therapy or enter W&W. Clinical updates were provided at 6 month intervals and patients were followed-up for a minimum of 12 months. Standard statistical methods were used to examine which factors were associated with initial disease management and those remaining on W&W long-term. Time to treatment was measured from date of diagnosis until date of first treatment, patients who had not commenced treatment were censored at the last date of follow-up.

Results:

Median age of all patients was 71 (range 32-92), 68.9% were male, 53.5% were MIPI high risk and median follow up 26 months. At baseline 67.3% of patients received upfront systemic therapy, 4.1% received localized radiotherapy, 1.0% were palliated and 27.6% were on W&W 90 days beyond diagnosis. Estimated 2-year OS of the whole population was 77.5%.

Patients on initial W&W tended to be older than those treated early (median 73 yrs vs. 71 yrs), had similar performance score (ECOG>1 OR 1.16, p=0.68) and no significant difference in WBC (WBC>15 OR 0.55, p=0.07). Although high risk MIPI was equally prevalent between the groups (OR 1.3, p=0.31) it was notable that no patient under 75 years was high risk in the observation group. Presence of measurable disease on CT discriminated between the two groups (OR 0.23, p=<0.001), but 71% of W&W had measurable disease indicating most were not the leukemic subtype. Markers of higher cell turnover, raised LDH and Ki67≥30%, were significantly less common in W&W patients (OR 0.32, p=<0.001; OR 0.3, p=0.001). 40% of women were put on W&W compared to 22% of men (OR 2.6, p=<0.001).

Of 87 patients followed on W&W 73.5% remained on observation at 1 year and 50.6% at 2 years, with median follow up 2.4 years. Univariate analysis revealed few baseline characteristics to be predictive for prolonged period of observation, in part relating to the low patient numbers, but key observations are displayed in figure 1. Patients with Ki67≥30% were less likely to remain on observation (HR 2.39, p=0.03), as were patients over 80 years old (HR 3.67, p=0.007), and those MIPI high risk compared to low risk (3.56, p=0.02).

Conclusion:

This study demonstrates the high prevalence of W&W in UK clinical practice and it provides reassurance to clinicians that half remain on observation beyond 2 yrs. LDH level and Ki67 status reflect the biological nature of disease and it is therefore not unexpected that lower levels predict for a more indolent course. However, with Ki67≥30 in 25% of patients observed beyond 2 years these measures alone are not sufficient to decide treatment. The tendency for older patients to be observed likely reflects a less aggressive clinical approach in patients with co-morbidities, and not the underlying biology. This explains the tendency for shortened observation period in older patients. The high prevalence of female patients in W&W is a striking observation that alludes to pathophysiological differences between the sexes that warrants further investigation.

Although the study highlights clinicians are increasingly at ease adopting W&W in MCL, it also demonstrates the need for better predictive markers of indolent disease. This study aims to achieve this with analysis of the collected tissue samples.

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