Fig. 1

Microscopic findings of the initial core-needle biopsy from the 50 mm soft tissue expansion adjacent to the chest wall. This lesion was initially believed to constitute a metastatic neuroendocrine carcinoma. All microscopic images are magnified × 200 unless otherwise stated. a. Routine hematoxylin and eosin staining depicting a tumor with a predominant solid growth pattern infiltrating the surrounding stroma. b. Routine hematoxylin and eosin section at × 600 magnification, illustrating nuclear pleomorphism. c. Widespread cytoplasmic synaptophysin immunoreactivity. d. Uniform CD56 immunoreactivity. e. Diffuse cytoplasmic insulinoma-associated protein 1 staining. f. Focal ISL LIM homeobox 1 nuclear staining (subsets of tumor cells). g. Negative staining for melanoma antigen. h. Negative staining for human melanoma black 45. i. Diffuse positivity for vimentin