DISCUSSION
Although there were several breakthrough innovations in treatment, such
as target therapy, or immune checkpoint inhibitors, oral cancer patients
with regional recurrence incurred grave outcomes.2,4Besides radical resection of primary tumor with adequate margin, the
next step was to perform an adequate neck dissection. Previous studies
had proved the positive association between LN yield and survival
rates.8,16 However, strategies to improve LN yield was
not clearly found in literatures. This study was the first to explore
the impact of LNPA among surgeons for quality of neck dissection.
Through continued education, promotion of importance of LN yield in neck
dissection surgery, identification of landmarks during surgery and
public announce of LN yield average to surgeons might promote the
quality of neck dissection and reduce regional recurrence in turn
through a difference-in-differences analysis. This soft and
non-mandatory method could be applied to all head and neck surgeons
widespread.
This study had several strengths. Using a difference-in-differences
analysis, the impact of policy or intervention change that was
implemented to some groups could be evaluated.13 In
this study, oral cancer patients were treated by two departments in our
institute, and LNPA was launched among target group in period after 2015
Oct. This situation provided us an opportunity to evaluate the possible
positive effect of LNPA on LN yield and regional recurrence through a
difference-in-difference analysis. Our finding of this study provided
evidences to support the positive effect of LNPA. In
difference-in-difference analysis, the coefficient for target group in
period after 2015 Oct was 13.4 (p<0.001). In regional
recurrence analysis, patients with cN0 disease might get borderline
benefit from LNPA with a reduction of regional recurrence rate of 9.4%
(p=0.087).
Although the study design of difference-in-differences analysis provided
us a chance to explore the effect of policy or intervention at different
times, several assumptions should be met. The most common assumptions
were the common trends assumption and strict exogeneity. The common
trend assumption meant that the unmeasured variables were time-invariant
group character or time-varying factors with group invariant
attributes.13 It could be examined by checking the
time-series graph with a set of parallel lines. Supplementary Figure
illustrated the changes of LN yield in different groups and periods. The
lines looked like parallel lines. Using matching techniques that could
eliminate possible selection bias between different groups and time
periods might help the difference-in-difference study, like the LNPA, to
reach the requirement of strict exogeneity.15 Other
matching method, such as refined covariate balance could also be
used.17
All national and international guidelines reported adequate LN yield
could significantly improve survival in oral cancer patients, but there
is no recommend intervention in clinical practice. Recently,
interventions based on the theories of behavior economics are summarized
by the acronym NUDGE and has been explored in the healthcare
field.18-20 Penn Medicine, for example, has used this
strategy widely. Changing the default in the choice of medicine greatly
increased the rate of prescriptions for generic
medicine.19 Using an active choice alert system in the
electric medical record increased the influenza vaccination rate 37% in
adults suitable for vaccination.21 Ayala et al. also
reported that moving from an ”opt-in” to an ”opt-out” system greatly
increased the rate of providing aspirin prophylaxis for preeclampsia
prevention.22 Automated dashboard with active choice
and peer comparison performance feedback to physicians had increased
statin prescribing for primary care physicians.23 In
our institute, several feasible and low-cost strategies were applied. At
first, weekly conferences were used to explain the association between
LN yield and recurrence since 2015 Oct. Thereafter, we encouraged the
surgeons to confirm important landmarks during neck dissections came.
Furthermore, the average number of LN yield was announced per month in
order to give feedback to the surgeons. Multiple NUDGE-like
interventions helped the target group to improve the cervical LN yield
in oral cancer surgery.
There are several limitations in this study. Although we introduced
several interventions to improve the quality of neck dissection in our
institution, the study was not completely prospective designed. Second,
we didn’t perform the survival analysis due to short-term of follow-up
period in those treated in period after 2015 Oct. The minimal follow-up
period in our series was 18 months, which represented the least
follow-up period for monitoring recurrence, and most of the recurrences
could be captured. Furthermore, we used the concept of regional
recurrence density, which meant the proportion of regional recurrence
among those with neck dissection during a specific period. Figure 3
illustrated the change of regional recurrence density among the target
group and control group. Through case matching with propensity score by
clinical tumor and node category, the comparison between the two groups
were more reasonable. Third, the spillover effects of LNPA to the
control group was not estimated. Although it was possible, the effect
might be minimal because these two departments located in different
floors in our institute.