PMC8248546_01
(A) Diagnosis: histological image of hematoxylin and eosin. section (scale bar: 50 microm) shows small tumor cells with a round-oval nucleus and poor cytoplasm that are very densely arranged in a diffuse pattern of growth. (B, C) Post-debulking surgery restaging: (B) Post-debulking clinical presentation with a purplish lesion (approximately 1.5 x 1.5 cm) situated near the right preauricular region close to the surgical scar. (C) Face and neck CT scan (axial projection) showing residual disease in the right preauricular region. CT, computed tomography.
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A diagnosis of MCC extended at the surgical resection margin was confirmed ( Figure 1A ). Additionally, MCPyV was not present. After 2 months, the patient returned for postsurgical restaging and a physical examination, which revealed an irregular purplish lesion of approximately 1.5 x 1.5 cm situated near the right preauricular region, close to the surgical scar ( Figure 1B ). CT of the face, neck, chest, and abdomen revealed malignant disease in the preauricular region ( Figure 1C ), including two pseudonodular areas, but showed no distant metastases. The patient then showed a reduction in NLR and LDH values concurrent with achieving a complete response after the first dose of avelumab (September 2019); these values continued to decrease after three cycles of avelumab, when complete response was radiologically confirmed ( Supplementary Table 1  and  Supplementary Figure 1 ).
Post-ECT restaging: (A) Post-ECT clinical presentation with an extensive, dark lesion (approximately 8.5 x 10.0 cm) in the preauricular and laterocervical regions. (B) Coronal (leftmost panel) and axial (right panels) CT scans showing extensive infiltrates in the subcutaneous tissues of the bilateral laterocervical region and right preauricular area. (C) Left to right: CT scan, FDG-PET scan, and CT and FDG-PET fusion images showing pathological accumulation in the preauricular area extending until the bilateral laterocervical and sternal level. (D) Total-body FDG-PET image confirming significant FDG uptake in mandibular, laterocervical, and sternal regions. (E) Hematoxylin and eosin stain (scale bar: 50 microm) of the tumor sample taken after ECT. Compared with the tumor sample collected before ECT, there was a decrease in neoplastic cellularity and edematous stroma. CT, computed tomography; ECT, electrochemotherapy; FDG-PET, 18-fluorodesossyglucose-positron emission tomography; MCC, Merkel cell carcinoma.
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After 1 week (at the beginning of July 2019), the erythematous lesion had increased substantially in size (8.5 x 10 cm) in the preauricular region and extended to the lateral cervical region ( Figure 2A ). CT scans confirmed disease progression and revealed extensive infiltrates, including in the pseudonodular areas, in the subcutaneous tissues of the bilateral lateral cervical region, and in the right preauricular area ( Figure 2B ); 18-fluorodesossyglucose-positron emission tomography (FDG-PET) confirmed pathological accumulation in the preauricular area extending to the bilateral lateral cervical and sternal level ( Figure 2C ), as confirmed by the whole body PET-FDG (  Figure 2D ). Additionally, biopsy and IHC staining of the preauricular cutaneous area showed a high-grade neuroendocrine tumor, confirming progression ( Figure 2E ).
Response to avelumab treatment: (A) Clinical presentation of substantial measurable reduction in lesion size after one dose of avelumab. (B) Clinical presentation of confirmed complete regression of the tumor mass after three doses of avelumab. (C) Face and neck coronal (leftmost panel) and axial (right panels) CT scans showing complete radiological response. (D) Clinical presentation of ongoing complete response on 30 October 2019. CT, computed tomography.
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After the first administration of avelumab, a substantial reduction in lesion size was observed with no measurable lesion remaining ( Figure 3A ). After three administrations of avelumab, a complete response was confirmed according to iRECIST (modified Response Evaluation Criteria in Solid Tumors guideline for immunotherapy) ( Figures 3B, C ). As of 30 October 2019, the patient was still continuing with avelumab flat dose 800 mg IV every 2 weeks, with CT scans every 3 months; he had an ongoing complete response, with no evidence of new lesions or progressive disease ( Figure 3D ).
Immunohistochemical staining of biopsy samples taken (A) during surgery and (B) after ECT. CD, cluster of differentiation; ECT, electrochemotherapy; HLA, human lymphocyte antigen; MHC, major histocompatibility complex; PD-1, programmed cell death protein-1; PD-L1, programmed cell death-ligand 1. Scale bar: 50 microm.
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The final scores obtained from the product of I x E, as described in the Material and Methods section, are summarized in  Table 2 .  Figure 4  shows the images related to the most important data resulting from immunohistochemical analysis performed on bioptic samples at diagnosis (Column A) and after ECT (Column B). 