chemokines or even synthetic scaffolds to in-
duce TLS formation in otherwise“noninflamed”
tumors ( 69 ). High expression of genes asso-
ciated with angiogenesis and B cell receptor
pathways was associated with prolonged RFS
after neoadjuvant anti–PD-1 therapy in a mela-
noma study (Table 1) ( 51 ), supporting the histo-
logic description of a tumor regression bed that
extends beyond a simple T cell signature. The
potential role of B-lineage cells in tumor re-
jection after anti–PD-1 therapy has been rela-
tively understudied. The expansion of B cells
after anti–PD-1 therapy is consistent with the
original basic functional description of the PD-1
pathway ( 70 ); however, their increased detec-
tion in the TME does not necessarily equate
with a requirement for tumor rejection. Addi-
tional research will be needed to define the
potential role of B cells in tumor regression
and to determine whether their contribu-
tions may be tumor type or context dependent
( 56 , 71 , 72 ). The above-described features of
robust inflammation and fibrosis in respond-
ing tumors have been shown to account for
apparent discrepancies between radiographic
and pathologic response assessments after neo-
adjuvant immunotherapy ( 45 , 52 , 66 , 73 ). Such
discrepancies may depend on the kinetics of
anti–PD-1 response in certain tumor types, in
the context of the neoadjuvant treatment inter-
val before radiographic restaging and surgery.
In cases in which definitive surgical resection
after neoadjuvant immunotherapy would result
in serious functional or cosmetic consequences—
for example, locally advanced gynecologic or
genitourinary carcinomas, or scalp or facial
tumors—it is possible that on-treatment biop-
sies could be used to assess therapeutic response
by using the above-described irPRC. These crite-
ria, originally developed for assessing response
to neoadjuvant anti–PD-1–based immunothera-
pies, have recently been applied to core needle
tumor biopsies taken from patients with ad-
vanced unresectable cancers while receiving
thesametherapies.Inamelanomastudy,such
assessments have already been shown to cor-
relate with 5-year OS ( 73 ), suggesting the poten-
tial for innovations in pathologic evaluation to
allow for prognostication, therapeutic decision
making, and organ sparing. Association of
irPRC with OS in this latter scenario supports
the concept that irPRC may ultimately be
correlated with long-term patient outcomes
in the neoadjuvant setting. Over time, more
advanced imaging tools may also become avail-
able to capitalize on the observed features of
the regression bed or otherwise more accu-
rately reflect the residual tumor burden.
Future development
More than 100 clinical trials of neoadjuvant
anti–PD-(L)1 therapy are now ongoing in di-
verse tumor types, in which anti–PD-(L)1 is ad-
ministered as monotherapy or in combination
with other immunotherapies, radiation ther-
apy, chemotherapy, kinase inhibitors, tumor-
targeted antibodies, or endocrine or metabolic
modulators [reviewed in ( 74 , 75 )]. Treatment
combinations designedto recruit more immune
cells into the tumor—such as intratumoral the-
rapies (oncolytic viruses or interferon path-
way agonists), cancer vaccines, and kinase
inhibitors—hold promise. Furthermore, treat-
ment combinations with increased antitumor
efficacy might accelerate response kinetics,
thus shortening the optimal presurgical treat-
ment interval. The first wave of neoadjuvant
trials has emphasized cancer types in which
anti–PD-(L)1 mono- or combination therapies
have already shown some efficacy in the ad-
vanced metastatic diseasesetting,hypothesiz-
ing that applying these treatments earlier in
the course of cancer evolution will be benefi-
cial. Early reports of safety and substantial pCR
rates from neoadjuvant combinations of anti–
PD-1 with anti–CTLA-4 ( 52 ), or with multidrug
chemotherapies for triple-negative breast can-
cer ( 76 , 77 )orNSCLC( 78 ), are encouraging but
require longer follow-up for assessment of clini-
cal efficacy endpoints. Next-generation trials
may assign patients to postsurgical observation
or intervention depending on the degree of
pathologic response, similar to the precedent
established with nonimmununologic neoadju-
vant therapies in breast cancer ( 79 ).
Although conventional computerized tomo-
graphic imaging at early time points on neo-
adjuvant therapy often underestimates the
extent of pathologic changes occurring in tumor
tissues, advanced methods for CT image analysis
and interpretation are currently under evalu-
ation and may provide previously unidentified
on-treatment markers of response to guide cli-
nical decision-making ( 80 , 81 ). Furthermore,
nuclear imaging with positron emission tomog-
raphy (PET) may operationalize markers spe-
cific for immune cells, checkpoint molecules, or
metabolic processes associated with neoadju-
vant treatment response or resistance ( 82 ).
Tumor specimens obtained after neoadju-
vant immunotherapy provide a rich source of
materials for in-depth scientific interrogations
that are expected to further illuminate mech-
anism of action for anti–PD-1 drugs. A sur-
prisingly high B cell component observed in
responding tumors has drawn attention to the
potentialroleofthiscelltypeincooperatingto
mediate anti–PD-1 responses. The quantity of
tissue obtained at surgery will allow much more
extensive single-cell analyses of on-therapy im-
mune responses within the TME, as well as
analyses of residual viable tumor cells, which
have been overlooked in many studies. It will
be ofgreat interest in the future to better
understand the particular characteristics of
these two compartments with regard to im-
munoarchitecture, cytokine signatures, and
cellular functional states, including tumor cellsignaling and immune evasion mechanisms in
cases with residual tumor. Findings from such
studies may reveal pathways, mechanisms, and
molecules that can be cotargeted in new treat-
ment combinations to increase the efficacy of
anti–PD(L)1 drugs.REFERENCES AND NOTES- S. L. Topalian, C. G. Drake, D. M. Pardoll, Immune checkpoint
blockade: A common denominator approach to cancer therapy.
Cancer Cell 27 , 450–461 (2015). doi:10.1016/
j.ccell.2015.03.001; pmid: 25858804 - M. Yarchoan, A. Hopkins, E. M. Jaffee, Tumor mutational
burden and response rate to PD-1 inhibition.N. Engl. J. Med.
377 , 2500–2501 (2017). doi:10.1056/NEJMc1713444
pmid: 29262275 - S. L. Topalianet al., Safety, activity, and immune correlates of
anti-PD-1 antibody in cancer.N. Engl. J. Med. 366 , 2443– 2454
(2012). doi:10.1056/NEJMoa1200690; pmid: 22658127 - P. T. Nghiemet al., PD-1 blockade with pembrolizumab in
advanced Merkel-cell carcinoma.N. Engl. J. Med. 374 ,
2542 – 2552 (2016). doi:10.1056/NEJMoa1603702;
pmid: 27093365 - S. L. Topalian, J. M. Taube, R. A. Anders, D. M. Pardoll,
Mechanism-driven biomarkers to guide immune checkpoint
blockade in cancer therapy.Nat. Rev. Cancer 16 , 275– 287
(2016). doi:10.1038/nrc.2016.36; pmid: 27079802 - S. L. Topalianet al., Five-year survival and correlates among
patients with advanced melanoma, renal cell carcinoma, or
non-small cell lung cancer treated with nivolumab.JAMA
Oncol. 5 , 1411–1420 (2019). doi:10.1001/jamaoncol.2019.2187;
pmid: 31343665 - C. Robertet al., Pembrolizumab versus ipilimumab in advanced
melanoma (KEYNOTE-006): Post-hoc 5-year results from an
open-label, multicentre, randomised, controlled, phase 3 study.
Lancet Oncol. 20 , 1239–1251 (2019). doi:10.1016/S1470-2045
(19)30388-2; pmid: 31345627 - J. Weberet al., Adjuvant nivolumab versus ipilimumab in
resected stage III or IV melanoma.N. Engl. J. Med. 377 ,
1824 – 1835 (2017). doi:10.1056/NEJMoa1709030;
pmid: 28891423 - A. M. M. Eggermontet al.,Adjuvant pembrolizumab versus
placebo in resected stage III melanoma.N. Engl. J. Med. 378 ,
1789 – 1801 (2018). doi:10.1056/NEJMoa1802357;
pmid: 29658430 - J. E. Gershenwaldet al., Melanoma staging: evidence-based
changes in the American Joint Committee on Cancer eighth edition
cancer staging manual.CA: Cancer J Clin 67 , 472-492 (2017). - P. Cortazaret al., Pathological complete response and long-
term clinical benefit in breast cancer: The CTNeoBC pooled
analysis.Lancet 384 , 164–172 (2014). doi:10.1016/S0140-
6736(13)62422-8; pmid: 24529560 - A. Pataeret al., Histopathologic response criteria predict
survival of patients with resected lung cancer after
neoadjuvant chemotherapy.J. Thorac. Oncol. 7 , 825– 832
(2012). doi:10.1097/JTO.0b013e318247504a; pmid: 22481232 - B. C. Carthonet al., Preoperative CTLA-4 blockade: Tolerability
and immune monitoring in the setting of a presurgical clinical
trial.Clin. Cancer Res. 16 , 2861–2871 (2010). doi:10.1158/
1078-0432.CCR-10-0569; pmid: 20460488 - A. A. Tarhiniet al., Immune monitoring of the circulation and
the tumor microenvironment in patients with regionally advanced
melanoma receiving neoadjuvant ipilimumab.PLOS ONE
9 , e87705 (2014). doi:10.1371/journal.pone.0087705;
pmid: 24498358 - E. R. Lutzet al., Immunotherapy converts nonimmunogenic
pancreatic tumors into immunogenic foci of immune
regulation.Cancer Immunol. Res. 2 , 616–631 (2014).
doi:10.1158/2326-6066.CIR-14-0027; pmid: 24942756 - J. Liuet al., Improved efficacy of neoadjuvant compared to
adjuvant immunotherapy to eradicate metastatic disease.
Cancer Discov. 6 , 1382–1399 (2016). doi:10.1158/2159-8290.
CD-16-0577; pmid: 27663893 - J. Liuet al., Timing of neoadjuvant immunotherapy in relation
tosurgery is crucial for outcome.OncoImmunology^8 ,
e1581530 (2019). doi:10.1080/2162402X.2019.1581530;
pmid: 31069141 - D. J. Lenschow, T. L. Walunas, J. A. Bluestone, CD28/B7
system of T cell costimulation.Annu. Rev. Immunol. 14 ,
233 – 258 (1996). doi:10.1146/annurev.immunol.14.1.233;
pmid: 8717514
Topalianet al.,Science 367 , eaax0182 (2020) 31 January 2020 7of9
RESEARCH | REVIEW