Fig. 3.

Characteristics of nodule; post-nivolumab treatment. a Thyroid core biopsy: hematoxylin/eosin. Normal follicular architecture with lymphocytic infiltrate and thin collagen bundles and initial fibrosis. Medium-power field. b Thyroid core biopsy: CD68 (histiocyte marker) immunohistochemistry. Aggregate of brown positive cells within the thyroid parenchyma. Medium-power field. c CD4 immunohistochemistry. Lymphocytes, subtype of T-cells, and histiocytes show positive stain. Medium-power field.