Neoadjuvant Nivolumab and Relatlimab in Merkel Cell Carcinoma

Pathological complete response rate

Proportion of patients with a pathological complete response, as determined on the week 6 surgical specimen using the guidelines published by the International Neoadjuvant Melanoma Consortium: Complete pathological response (pCR) = 0% viable tumour cells in the surgical specimen

Pathological non-complete response rate to neoadjuvant immunotherapy

Proportion of patients with each non-pCR response category, as determined on the week 6 surgical specimen using the guidelines published by the International Neoadjuvant Melanoma Consortium: * Near complete pathological response - (near pCR) - \>0% - ≤10% viable tumour * Partial pathological response (pPR) - \>10 - ≤50% viable tumour * Non pathological response (pNR) - \>50% viable tumour

Toxicity and tolerability of neoadjuvant immunotherapy

The treatment related adverse events (AE) as described in CTCAE version 5.0, from the initiation of study treatment up to 135 days after the last dose of study treatment

Objective response rate to neoadjuvant immunotherapy

The proportion of patients within each response category, as assessed using RECIST version 1.1, comparing week 6 to baseline CT and MRI. Objective response rate= CR and PR

Metabolic response rate to neoadjuvant immunotherapy

The proportion of patients within each response category, as assessed using PERCIST (standardised uptake value \[SUV\]) comparing week 6 to baseline PET. Metabolic response rate = CMR and PMR.

Polyomavirus positivity

1. Proportion of patients with and without polyomavirus in tumour tissue at baseline. 2. Correlate Merkel cell polyomavirus viral positivity (MCPyV+) in stage I-III MCC with pathological response.

Biomarkers of response, resistance, toxicity

* Morphological assessment H\&E, including viable MCC cells, Ki67, TILs density, % fibrosis, % necrosis, compared with paired baseline measures. * Tumour PD-L1 expression status (+ve status = ≥1% tumour cells positive staining using Dako 28-8 PD-L1 IHC assay). * Characterisation of immune profile in tumour microenvironment using multiplex immunohistochemistry and Imaging mass cytometry. * RNA sequencing - gene expression profile including potential to perform single cell analysis on dissection specimen from tumour dissociates (single cell RNA seq). * Characterisation of peripheral immune profile through Cytometry by time of flight. * DNA sequencing to determine tumour mutational burden and key somatic mutations. * Response to treatment using circulating tumour DNA in peripheral blood using droplet digital PCR to quantify tumour DNA (copies/ml plasma) of known mutation in MCC tissue.

Correlation of gut microbiome on outcomes

1. Correlation of bacterial diversity and abundance with treatment response and incidence of treatment-related toxicities 2. Correlation of self-reported dietary habits (including use of oral probiotics) at baseline and impact on bacterial diversity in the gut 3. The use of antibiotics and/or steroids during neoadjuvant treatment and the impact on intestinal bacterial diversity and abundance

Correlation of outcome measures

Proportion of patients with concordance in pathological response, RECIST response and metabolic response (PERCIST)