case_images: PMC11805602_01
case_images: Histological features of Merkel cell carcinoma. (A and B) Microscopic features of MCC on hematoxylin-eosin staining (4x and 10x high-power-field (HPF), respectively). (C and D) The tumor showed CK20 paranuclear dot-like staining, along with positive staining for CD56, chromogranin, and synaptophysin (4x and 10x HPF, respectively).
case_images: cureus-0017-00000077152-i01.jpg
case_images: PMC11805602_01_cureus-0017-00000077152-i01.jpg
case_images: FIG1
case_images: Immunohistochemistry showed CK20 paranuclear dot-like staining and neuroendocrine features, including chromogranin and synaptophysin (Figure 1).
case_images: Initial magnetic resonance imaging . MRI images show the left arm tumor and its relationship with the vasculonervous structures of the humeral bundle and axillary lymphadenopathy, respectively. (A) T2 sequence. (B) T1 sequence.
case_images: cureus-0017-00000077152-i02.jpg
case_images: PMC11805602_01_cureus-0017-00000077152-i02.jpg
case_images: FIG2
case_images: A magnetic resonance imaging (MRI) revealed a 5.7 x 4.9 cm lesion on the inner side of the left arm involving the vasculonervous structures of the humeral bundle and axillary lymphadenopathy measuring 3.7 x 2.6 cm (Figure 2).
case_images: After-treatment MRI. MRI after completing six cycles of nivolumab shows a reduction in the size of the lesion in the left arm and no signs of axillary lymphadenopathy. (A) T2 STIR sequence. (D) T1 sequence.
case_images: cureus-0017-00000077152-i03.jpg
case_images: PMC11805602_01_cureus-0017-00000077152-i03.jpg
case_images: FIG3
case_images: A follow-up MRI was performed, revealing a persistent lesion on the inner side of the left arm, measuring 2.8 x 1.6 cm, in contact with the vasculonervous structures of the humeral bundle, with no evidence of the previously noted axillary lymphadenopathy (Figure 3).