In order to fulfil their medical and academic mission, clinical trials have to be available to the very populations they are intended to serve. A broad and homogenous geographic distribution is thus paramount to ensure patient fairness as well as to allow optimal generalizability of trial results to real-world populations. We aimed to investigate trends in the geographic distribution of clinical trials in lymphoma performed over the past 2 decades.


We systematically searched the Clinicaltrials.gov registry for phase 3 and 4 clinical trials in lymphoma conducted between 01/01/1997 and 12/31/2017. We divided the time period into two intervals and analysed the geographic distribution of trials during these time periods. The Gini coefficient, a statistical measure of inequality ranging from 0 (equal distribution) to 1 (most unequal distribution), was calculated for each period.


We found 633 clinical trials in lymphoma conducted between 1997 and 2017 globally. 284 and 349 trials were performed in the 1997-2007 and 2008-2017 time periods, respectively. 127 (50%) and 138 (39.5%) of the trials were done in the US. Hodgkin Lymphoma accounted for 55 (19.3%) and 42 (12.0%) studies in the two time periods. CA, TX, IL and NY were consistently in the upper one-fifth of trial-abundant states (each accounting for 3.5-4.5% of all trials). AK, WY, MT and RI were consistently in the lower one-fifth of trial-abundant states (each accounting for 0.13-0.84% of trials). The trial participation of NY and AK mildly increased during the time period while that of TX and RI decreased. In each of the time periods, the 12 most trial-intense states accounted for 41.5% of all investigations. The 12 least trial-intense states were responsible for 8.8% of all the trials. The extent of geographic inequality increased over the years with the Gini coefficient rising from 0.246 to 0.3 between the first and second study period. The geographical pattern of state-specific trial intensity was strongly mitigated after adjusting for each state's population size.


The geographic distribution of clinical trials in lymphoma in the U.S is not uniform. Our data suggests that the trend of geographic mal-distribution is worsening, a phenomenon that may lead to deleterious public health outcomes. As patients' enrolment continues to be linked to geographic factors, patients' ability to enter clinical trials may be limited and the representation of real-world participants may be skewed (towards particular zip codes, socio-economical status and education levels, etc), consequently affecting the yield and generalizability of clinical trials. Innovative solutions must be devised to minimise any barriers to trial participation for suitable patients.


No relevant conflicts of interest to declare.

Author notes


Asterisk with author names denotes non-ASH members.