Introduction
Mucosal melanoma is a rare subtype of melanoma, accounting for 1.4% of melanoma diagnoses
in the United States.
1
Median overall survival from time of diagnosis for mucosal melanoma has historically
been less than that of cutaneous melanoma in part owing to the frequency of occult
presentation and the relative lack of evidence-based guidelines specific to mucosal
histology.
2
Radiation therapy (RT) in mucosal melanoma has shown promise in certain settings but
indications remain poorly defined.
3
,
4
Immune checkpoint inhibitors have shown excellent response rates in metastatic melanoma
and are increasingly used for mucosal melanoma; however, most patients will eventually
progress. Response patterns are highly variable among patients who respond to immunotherapy.
Although a small group of patients will experience complete response, many patients
will have other types of responses such as pseudoprogression (disease enlargement
followed by shrinking) or oligoprogression (progression at a limited number of sites).5,
6, 7 Patients with oligoprogression after treatment are of particular interest owing
to the possibility of controlling the progressive disease with local therapy and achieving
long-term survival. This concept has been demonstrated in retrospective studies of
patients with melanoma; however, there have been no studies demonstrating this for
patients with mucosal melanoma.
5
,
8
Herein, we report a case of a 67-year-old woman with metastatic anorectal mucosal
melanoma with primary site oligoprogression on nivolumab who was treated with RT to
the primary site, which induced a complete, durable, and ongoing response of almost
3 years.
Case Presentation
The patient was a 67-year-old woman who initially presented with complaints of difficulty
emptying her bowels. A colonoscopy revealed a tumor in her rectum, located 1.0 cm
from the anal verge. A biopsy was consistent with primary melanoma of the anus, BRAF
wild-type. Further staging workup included a computed tomography (CT) of the chest,
abdomen, and pelvis with intravenous contrast (Fig 1), followed by a positron emission
tomography (PET)/CT scan 1 week later (Fig 2). The primary lesion was noted to be
2.3 × 2.3 cm with a standardized uptake value (SUV) of 11.1 and with marked thickening
of the wall of the anorectum with extension to the anus. Two perirectal lymph nodes
were noted (1.6 and 2.1 cm), in addition to 1 lymph node seen above the rectum just
posterior to the sigmoid colon (1.5 × 1.0 cm). CT also revealed multiple low-density
lesions in the liver: 1.1 cm and 1.0 cm in the right lobe (SUV 6.4) and 1.2 cm in
the left lobe. A “left peri-rectal mass” was noted with an SUV of 12.8. An additional
1.2 cm presacral lymph node was noted with an SUV of 4.3. Hyperavidity was also noted
in the right sacrum and right iliac bone (SUV 3.1). Biopsy of a liver lesion was performed
and confirmed metastatic melanoma. Magnetic resonance imaging (MRI) of the head with
intravenous contrast was negative for intracranial disease. Interval CT 4 weeks after
initial imaging revealed an increase in the size of the primary to 2.5 cm, a bilobed
perirectal mass 4.7 × 2.6 cm, and a new indeterminate 6-mm nodule in the right middle
lobe of the lung.
Figure 1
Initial staging computed tomography (CT) with contrast (A = axial, B = coronal, C
= sagittal).
Figure 2
Initial staging positron emission tomography (PET)/computed tomography (CT).
Given her stage IV disease, she was started on combined ipilimumab and nivolumab on
the Eastern Cooperative Oncology Group-American College of Radiology Imaging Network
EA6141 clinical trial; she was randomized to the control arm and did not receive sargramostim.
After approximately 6 weeks of treatment, she developed mild hypophysitis and ipilimumab
was discontinued and she was maintained on nivolumab alone every 2 weeks.
Ten weeks after starting treatment, interval restaging imaging was obtained with a
CT of the chest, abdomen, and pelvis with intravenous contrast. The previously noted
indeterminate right middle lobe nodule appeared to be nearly completely resolved.
The liver metastases appeared significantly smaller. No new liver lesions were noted.
The pelvic and presacral lymph nodes appeared much improved without any new adenopathy.
The maximum thickness of the anorectal primary had decreased from 2.5 cm to 1.8 cm.
Interval imaging 12 weeks later continued to show stable findings of treatment response
with a stable hypodensity in the left lobe of the liver, no lesions in the right lobe
of the liver, stable pelvic lymph nodes, and the primary appearing similar in size
compared with prior. The previously noted left perirectal mass was also smaller (1.1
× 0.9 cm, previously 1.3 × 1.0 cm).
Follow-up CT imaging at 8 months after treatment initiation suggested progression
of disease at the primary site with distant disease control. The anorectal mass had
enlarged from 1.8 × 2.5 cm to 2.2 × 3.3 cm. Multiple pelvic lymph nodes appeared slightly
larger. Enlarging left and right inguinal nodes measuring 1.2 cm were noted representing
a change compared with prior studies. The right liver mass continued to be nondiscernable
and the left liver lesion was stable in size. An MRI of the pelvis with intravenous
contrast (Fig 3) was obtained that elaborated an infiltrative tumor. A T2 enhancing
mass was seen in the anus and lower rectum with transmural extension, invasion of
the levator ani muscle on the right laterally, and extension through the pelvic floor
musculature anteriorly. Abnormal tissue tracking cephalad was noted on the left, consistent
with the infiltrating tumor. Overall, the findings were interpreted as representing
progression of disease at the anorectal primary and adjacent lymph nodes and the patient
was taken off trial. She was continued on maintenance nivolumab and referred to radiation
oncology for consideration of local therapy, given her worsening symptoms of constipation
and occasional bleeding. Clinically, rectovaginal septum induration secondary to malignancy
was also appreciated at this time.
Figure 3
Preradiation therapy (RT) magnetic resonance imaging (MRI) with contrast (A = axial,
B = coronal, C = sagittal).
It was decided to deliver consolidative RT without interruption of maintenance nivolumab.
Nine months after starting initial immunotherapy, 45 Gy in 3 Gy per fraction was delivered
using a 3-field 3D conformal technique to the diagnostic MRI and CT simulation-defined
primary site gross tumor volume with a 2.0 cm circumferential margin and a 3.0 cm
superior/inferior margin without regional coverage (Fig 4). This was felt to be a
regimen that would achieve a near definitive effective dose while being safe for the
anal canal, with hypofractionation enabling a shorter treatment time and assisting
in overcoming resistant melanoma.
Figure 4
Radiation therapy treatment plan dose distributions (isodose curves).
RT was tolerated without issue. Interval CT imaging 3 months later demonstrated significantly
decreased thickness of the primary anorectal lesion measuring 1.3 cm compared with
2.3 cm previously; perirectal lymph nodes also appeared smaller in size. MRI imaging
5 months after RT demonstrated circumferential submucosal thickening involving the
distal rectum and anus without enhancing lesion, thought to be consistent with postradiation
change; no lymphadenopathy was seen (Fig 5). A linear enhancing band extending from
the anterior aspect of the anus through the external sphincter to the lower vagina/vulvar
area was visualized and thought to represent a fistulous tract. Clinically, the patient
reported improvement in caliber of stools. Serial CT, MRI, and interval MRI 6, 11,
and 19 months after RT, respectively, continued to show stable findings.
Figure 5
Five months post-radiation therapy (RT) magnetic resonance imaging (MRI) with contrast
(A = axial, B = coronal, C = sagittal).
A PET/CT obtained 21 months after RT showed minimal residual uptake in the anal canal
with no associated mass. An interval PET/CT 4 months later showed stable (SUV 4.6)
uptake in the region of the anal canal with no associated mass. A third interval PET/CT
was obtained after a subsequent 8 months (33 months after RT and 42 months after the
start of initial treatment), showing no areas of hypermetabolism. The patient’s nivolumab
was discontinued. The patient has enjoyed excellent performance status and has been
without symptom or complaint.
Discussion
This case shows complete and durable response of metastatic anorectal mucosal melanoma
to RT after primary site progression on nivolumab. Although there was radiographic
concern for fistula after radiation, the patient has done well clinically, has not
required any intervention for it, and it has improved over time.
This is a case of “oligoprogression” and supports the hypothesis that prolonged survival
may be possible with treatment of limited progressive sites, similar to the paradigm
that has been demonstrated in a prospective study of oliogmetastatic disease.8, 9,
10, 11 The optimal management of oligoprogressive patients on immune checkpoint inhibitors
remains poorly defined owing to the lack of prospective data. A PubMed search for
the terms “oligoprogression” and “melanoma” yields only 2 results, both of which are
retrospective and neither of which are specific to RT.
5
,
8
In the larger of the 2 retrospective studies, 52 patients met inclusion criteria of
initial treatment with immune checkpoint inhibitor followed by progression at 1 to
3 sites. These patients were treated with a variety of local therapies. Three-year
progression-free survival was 31%. Interestingly, improved progression-free survival
was found in those with progression limited to previously established tumors.
8
Extrapolating these results to the presented case is difficult given the various other
local therapy options included in their analysis such as ablation, surgery, and stereotactic
body radiation therapy. This suggests that an optimal consolidative approach to oligoprogression
may yet be elucidated, and our case highlights the potential of radiation immunotherapy
combination in this situation. The excellent response of the patient in this case
raises the possibility that RT may have advantages over other forms of local therapy
when used in oligoprogressive patients receiving immune checkpoint inhibitors. One
hypothesis for this synergy is the immunogenic effects of radiation, which include
increased neoantigen expression, activation of the “cyclic GMP-AMP synthase/stimulator
of interferon genes” pathway, and increased dendritic cell activation.
12
Given the strong biological rationale for the combination of radiation and immunotherapy
13
and the observation of such synergy in preclinical models,
14
treatment with both modalities is being investigated in numerous clinical trials (Table 1).
Given that our patient only had 1 oligoprogressive site, a nontarget site was not
available at which an abscopal response to RT could be assessed. Observation of such
an effect would have strengthened our ability to conclude RT-immunotherapy synergy
was involved.
15
Table 1
Summary of relevant ongoing immunotherapy + melanoma clinical trials
NCT number
Title
Immunotherapy
Radiation
Phase
Estimated enrollment
Patient characteristics
Mucosal histology included
Primary outcome
Estimated start date
Estimated primary completion date
Estimated final completion date
NCT03758729
Phase II Study of Nivolumab in Combination With Radiation Therapy as Definitive Treatment
for Patients With Locally Advanced, Unresectable Head and Neck Mucosal Melanoma
Nivolumab
2 Gy × 35
Single arm, phase II
26
Locally advanced, unresectable H&N mucosal melanoma
Yes, trial is specific for mucosal melanoma
Response rate (CR + PR)
September 1, 2019
March 2020
December 2020
NCT03646617
Ipilumumab and Nivolumab With or Without Hypofractionated Radiation Therapy in Patients
With Metastatic Melanoma (RadVax)
Ipilumumab + nivolumab
8 Gy × 3 versus no radiation
Phase II
70
Metastatic melanoma, ECOG 0-1
Not specified
Safety
August 23, 2018
February 23, 2022
February 23, 2023
NCT04042506
SBRT as a Vaccination for Metastatic Melanoma
Nivolumab
8-10 Gy × 3
Single arm, phase II
15
Unresectable melanoma (any histology)
Yes
Safety
August 2019
March 2023
March 2028
NCT03340129
Anti-PD 1 Brain Collaboration + Radiation Therapy Extension (ABC-X Study)
Ipilumumab + nivolumab
SRS 16-22 Gy up-front versus salvage
Phase II
218
Cutaneous, acral, or mucosal melanoma with 1 or more brain metastases
Yes
Neurologic death
August 14, 2019
August 2022
August 2024
NCT04017897
The Combination of Anti-PD-1 With Radiation Therapy in Previously Untreated Metastatic
Melanoma
Ipilumumab + nivolumab
Not specified
Phase II
52
Unresectable stage III - IV melanoma, ECOG <1, no prior systemic therapy
Yes
Overall response rate
July 3, 2019
July 2022
July 2022
NCT03850691
Radiation and Combination Immunotherapy for Melanoma
Aldesleukin + nivolumab OR Aldesleukin + ipilumumab + nivolumab
Not specified
Phase II
44
At least 3 radiographically distinct lesions (>1.5 cm) previously refractory to standard
immunotherapy
No
Objective response rate, safety
May 28, 2019
December 2025
December 2025
NCT03354962
Induction of Immune-mediated aBscOpal Effect thrOugh STEreotactic Radiation Therapy
in Metastatic Melanoma Patients Treated by PD-1 + CTLA-4 Inhibitors (BOOSTER MELANOMA)
Ipilumumab + nivolumab
SBRT versus no radiation
Phase I/II
120
Histologically proven unresectable stage III-IV melanoma. PD-L1 expression <1%
Yes
Dose limiting toxicities, abscopal effect
October 15, 2018
September 2022
March 2024
Abbreviations: CR = complete response; CTLA-4 = cytotoxic T-lymphocyte associated
protein-4; ECOG = Eastern Cooperative Oncology Group; H&N = head and neck; OR = overall
response; PD-1 = programmed cell death protein 1; PR = partial response; SBRT = stereotactic
body radiation therapy; SRS = stereotactic radiosurgery.
It is notable that we achieved durable control given the mucosal histology in this
case. Mucosal melanoma differs from cutaneous melanoma in presentation, diagnosis,
and genetic profile.
16
,
17
Surgery with the potential to achieve negative margins is considered standard of care
for these patients; however, this is often not feasible owing to anatomic location
and the higher frequency of metastatic disease at presentation compared with cutaneous
melanoma.
17
,
18
Other treatment options are similar to those available for cutaneous melanoma including
radiation, chemotherapy, targeted small molecule inhibitors, and immunotherapy.
19
Notable differences in treatment involve the types of inhibitors available and the
response to immunotherapy. Mucosal melanomas more frequently harbor KIT mutations
as opposed to the BRAF mutations seen in cutaneous melanoma.
20
,
21
Retrospective studies have shown that the utilization of immunotherapy is increasing
and it may provide superior results in mucosal melanoma compared with other treatment
modalities, especially when combined with RT.
22
,
23
Response to immunotherapy, however, may also be lower for mucosal melanoma than for
cutaneous melanoma, possibly owing to lower levels of tumor neoantigens.
24
A large retrospective study showed objective response rates to nivolumab of 23.3%
and 40.9% for mucosal and cutaneous melanoma, respectively.
25
Given the decreased immunogenicity of mucosal melanoma and the ability of radiation
to enhance immunogenicity,
12
,
24
melanoma with mucosal histology may derive great benefit from the addition of RT to
immunotherapy. A retrospective study of 23 patients with head and neck mucosal melanoma
treated with RT and immunotherapy reported target local control was highest with an
RT and immunotherapy combination (94% at 1 year).
23
A prospective study of an RT/immunotherapy combination in this histology is ongoing
with patients with mucosal melanoma included in many melanoma clinical trials (Table 1).
26
,
27
Conclusions
Our illustrative single-case experience suggests the dramatic and durable control
that may be achieved with a consolidative radiotherapeutic approach to oligoprogression
on immunotherapy in a case of a typically poorer responding mucosal melanoma. The
management of such patients remains poorly defined. Randomized trials investigating
methods of controlling disease progression in the setting of immunotherapy are necessary.