Thymus carcinoid.

A carcinoid of the thymus was studied by light- and electron-microscopy, immunohistology and flow-cytometry. The tumor showed a ribbon- and festoon-like growth-pattern with foci of necrosis, invasion of vessels and infiltration of mediastinal lymph nodes. The cytoplasma of the tumor-cells contained neuroendocrine granula and immunohistochemistry of ACTH was positive. The tumor-cells were connected by desmosomes, correlating to a pre-keratin positive immunohistology. In flow-cytometry the tumor-cells showed a near haploid DNA aneuploidy which is an extremely rare finding in solid tumors and in the few cases described indicative for treatment resistance.