Bayesian Analysis of a Patient with either Recurrent Metastatic Melanoma or Ipilimumab-Induced Sarcoidosis

Abstract

A patient with metastatic melanoma received treatment with adjuvant Ipilimumab and subsequently developed signs of sarcoidosis 6 weeks post completion of treatment. 18 F FDG PET CT was completed which described FDG avid hilar and mediastinal adenopathy and bilateral FDG avid lung nodules with low-grade bilateral uptake in the lower limbs. Differential diagnosis was either recurrent melanoma or sarcoidosis arising as an immune related adverse event attributable to Ipilimumab. Prior to initiation of anti- PD-1 treatment we assessed the merit of undertaking a biopsy to confirm a second relapse of metastatic melanoma. We approached a quantitative appraisal of the clinical dilemma arising in this case using Bayes' theorem and a meta-analysis of published literature of the accuracy of PET detection of recurrent cutaneous melanoma. Partly on this rationale a bronchoscopic biopsy of two lymph nodes was undertaken. Results found abundant histiocytic aggregates focally forming granuloma giving a diagnosis of Ipilimumab induced sarcoidosis. Therefore, positive findings on PET imaging in patients with melanoma treated with Ipilimumab can represent other entities including iatrogenic sequelae from immunotherapy. With the emergence immunotherapy. With the emergence of novel immunotherapy treatment for metastatic melanoma and an increase in the popularity of PET imaging as a modality for diagnosing metastatic disease this article highlights two important issues; the traditional role of biopsies in confirming metastatic disease and immune related adverse events associated with novel therapies.