4. Discussion
In this single institution, retrospective study we identified an
association of involvement of deep margins at biopsy with residual
melanoma at the time of wide local excision. Ulceration and absence of
TILs at biopsy for stage I and II melanoma patients were independently
associated with increased risk for disease progression. Notably, the
hazard ratio for absence of TILs was 9 using the best Cox-proportional
hazards model, suggesting that patients with absent TILs have a 9x
increased risk of progression relative to patients with present TILs.
That is over half the hazard ratio for ulceration, which is a
well-established risk factor incorporated into staging, found by the
same model. While the number of absent TIL patients in our study was
small, the magnitude of the effect suggests it warrants further study.
The recent Keynote-716 study suggests that some lower stage melanoma
patients could benefit from early adjuvant immunotherapy [8]. The
identification of absent TILs could be used as a readily available
indicator of high-risk disease in stage I-II patients who may be more
likely to benefit from early intervention. The caveat is that commonly
used immunotherapies rely on lymphocytic infiltration for clinical
efficacy [20-22]. Thus, patients with absent TILs may also be
resistant to immune checkpoint inhibitors, which in part could explain
their worse overall prognosis.
An alternative approach is to consider absent TILs indicative of a
“cold” melanoma. Though melanoma is conventionally considered a
“hot” tumor, patients with absent TILs may benefit from strategies
that convert immunologically “cold” tumors to “hot” [23].
Incorporating agents that boost immune infiltration into the tumor are
likely essential for these patients to benefit from immunotherapy.
Zakharia et al combined indoximod, an indoleamine 2,3-dioxygenase
inhibitor (IDO) inhibitor, with pembrolizumab in patients with advanced
melanoma, resulting in an objective response rate of 51% [24]. IDO
depletes tryptophan from the extracellular environment, and increased
expression of IDO has been shown to decrease T cell infiltration in
colorectal cancer [25]. The TLR-7/8 agonist imiquimod has been
demonstrated to increase T cell infiltration and activation for squamous
cell carcinoma of the skin [26]. Imiquimod has also been used for
melanoma-in-situ with positive margins with an estimated 95% resolution
of residual melanoma-in-situ [27]. Case series suggest that
imiquimod stimulates T cell infiltration in the context of
melanoma-in-situ [28], raising the possibility that imiquimod could
improve the outcomes of patients with absent TILs on biopsy. Imiquimod
is well tolerated with few side effects and warrants consideration as
neoadjuvant treatment for early stage melanomas [29]. Treatment with
agents like imiquimod to enhance T cell tumor infiltration, either as
monotherapy or in combination with immunotherapy, may improve outcomes
in stage I and II patients with absent TILs.
Our study has several limitations. A major limitation is the small
sample size (68 patients), which is further compounded by missing data
from some biopsy reports (Table 2 ). Furthermore, the relatively
small sample size prevented us from evaluating associations between
lymphocyte status and response to immunotherapy in patients that
recurred. Despite this limitation, our results suggest absent
lymphocytes and ulceration identify early stage melanoma patients at
higher risk for progression and should be confirmed in a larger study.
To do this, we are expanding the scope of this retrospective study to
include all evaluable patients within a clinical research database
available at our institution. This larger, multi-institutional study
could elucidate whether absent lymphocyte status predicts tumor
resistance to immune checkpoint inhibitors in early stage patients. Like
all retrospective studies, our analysis identifies associations, but we
cannot infer causal relationships. Additionally, this study only
analyzes patients seen at the an academic tertiary care center.
Cheraghlou et al demonstrated that treatment for early stage melanoma at
hospitals with an academic affiliation or high-volume is associated
improved survival compared to those treated at non-academic or
low-volume centers [30]. A prospective study treating patients with
imiquimod after wide local excision would determine 1) if absent TIL
status can be reversed pharmacologically and 2) whether recruitment of
TILs improves progression free survival in early stage melanoma
patients.
5. Author contributions:KM contributed to conceptualization, study design, data collection, data
interpretation, manuscript writing and review. TE, VA, and EM
contributed to data collection, data interpretation and manuscript
writing. ZG and JHL performed statistical analyses and manuscript
review. BD contributed to conceptualization, study design, data
interpretation, manuscript writing, and manuscript review. All authors
approved the final version of the manuscript for submission.
6. Data availability: The de-identified datasets generated
during and/or analysed during the current study are available from the
corresponding author (BD) on reasonable request.