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CLINICAL REPORT
Circulating Tumour DNA for Monitoring Treatment Response to
Anti-PD-1 Immunotherapy in Melanoma Patients
Atsuko ASHIDA, Kaori SAKAIZAWA, Hisashi UHARA and Ryuhei OKUYAMA
Department of Dermatology, Shinshu University School of Medicine, Matsumoto, Japan
Anti-programmed cell death-1 (anti-PD-1) antibody
shows high therapeutic efficacy in patients with ad-
vanced melanoma. However, assessment of its thera-
peutic activity can be challenging because of tumour
enlargement associated with intratumoural inflamma-
tion. Because circulating tumour DNA (ctDNA) corre-
lates with tumour burden, we assessed the value of
ctDNA levels as an indicator of tumour changes. Quan-
tification of ctDNA (BRAF mutant or NRAS mutant ) levels by
droplet digital PCR in 5 patients with BRAF or NRAS
mutant melanoma during the treatment course sho-
wed dynamic changes corresponding to radiological
and clinical alterations. In 3 cases in which the anti-
PD-1 antibody was effective, ctDNA levels decreased
within 2–4 weeks after treatment initiation. In 2 cases
in which the anti-PD-1 antibody was ineffective, ctDNA
levels did not decrease after treatment initiation. ct-
DNA could be a useful biomarker to predict early re-
sponse to treatment in patients with advanced mela-
noma treated with anti-PD-1 immunotherapy.
Key words: melanoma; circulating tumour DNA; anti-program-
med cell death-1 antibody; BRAF; NRAS; droplet digital PCR.
Accepted Jul 5, 2017; Epub ahead of print Jul 6, 2017
Acta Derm Venereol 2017; 97: 1212–1218.
Corr: Ryuhei Okuyama, Department of Dermatology, Shinshu University
School of Medicine, 3-1-1 Asahi, Matsumoto 390-8621, Japan. E-mail:
[email protected]
I
n the advanced stages, melanoma is among the most
aggressive and treatment-resistant cancers and its
incidence is increasing worldwide. Substantial progress
has been made recently in the treatment of advanced
melanoma. Immune checkpoint blockade is recommen-
ded as the first-line therapy for patients with metastatic
or unresectable melanoma. Monoclonal antibodies
against programmed cell death-1 (PD-1) and cytotoxic
T-lymphocyte-associated protein-4 (CTLA-4) showed
remarkable long-term benefits in 40% and 10% of pa-
tients, respectively (1, 2). These antibodies act directly
on the immune system, rather than on the tumour, and
the kinetics of tumour regression may be delayed. In
some cases, tumours assessed using computed tomo-
graphy (CT) imaging appear to enlarge during therapy
before regressing. In other patients, new tumours appear
during therapy and later regress. The apparent tumour
doi: 10.2340/00015555-2748
Acta Derm Venereol 2017; 97: 1212–1218
progression may, in some cases, reflect intratumoural
inflammation rather than actual tumour growth. Despite
considerable progress in the treatment of melanoma, re-
liable markers to predict treatment response or evaluate
early recurrence are lacking. Non-invasive indicators
of changes in tumour burden could provide early infor-
mation about potential therapeutic outcomes, thereby
preventing potentially serious immune-related adverse
events in patients with true disease progression.
Serum lactate dehydrogenase (LDH) is widely used as
a surrogate marker of tumour progression in melanoma
(3). Elevated LDH level is associated with a high disease
burden and poor survival. However, because LDH occa-
sionally remains within the normal range despite tumour
progression, its value as a biomarker is limited. In addi-
tion, LDH increases in response to many conditions, such
as infections, liver dysfunction, and myocardial disorders
among others, and in malignancies other than melanoma.
Circulating tumour DNA (ctDNA) in the peripheral
blood is a novel biomarker for evaluating tumour featu-
res in patients with advanced cancer. Cell-free DNA is
released from both normal and tumour cells via a variety
of mechanisms, including apoptosis and necrosis. ctDNA
contains the same genetic alterations present in the source
tumour (4–6). In particular, ctDNA with mutations in
EGFR, KRAS, or BRAF is detected in cancer patients,
and the detection of mutations in ctDNA is under in-
vestigation as a specific biomarker for the diagnosis and
monitoring of patients with different cancer types (7–11).
Mutations of BRAF and NRAS are common in melanoma:
the frequency of BRAF mutations, chiefly BRAF V600E , is
50–60% in Caucasians and 20–30% in Asian popula-
tions (12–14); and that of NRAS mutations is 15–25%
in Caucasians and 7–10% in Asian populations (14–16).
Therefore, BRAF-mutated and NRAS-mutated ctDNAs
are potentially useful biomarkers for melanoma.
In the present study, dynamic changes in ctDNA were
analysed in parallel with measurement of LDH levels in
melanoma patients during treatment with anti-PD-1 anti-
body. Droplet digital PCR (ddPCR) technology, which
can be readily used to quantify mutant DNA copies, was
used to examine changes in mut