CD5

CD56

IHC CK:POSITIVE NSE:POSITIVE EMA:POSITIVE CHROMOGRANIN:POSITIVE S100:NEGATIVE SYNAPTOPHISIN:POSITIVE CD56:POSITIVE KI67:POSITIVE IN 10% OF NUCLEI CD5:NEGATIVE

DIFFERENTIAL DIAGNOSIS -Carcinoid tumor -Thymic carcinoma -Neuroendocrine carcinoma -Type A thymoma -Paraganglioma

CARCINIOD TUMOR -Malignant neoplasm that often invades locally and metastasizes distantly -usually lacks endocrine manifestation -component of MEN type1 , NF1 -more aggressive neoplasm than bronchial carcinoid,,,fall into the category of atypical carcinoid tumor

CARCINOID TUMOR Grossly, thymic carcinoid is solid, usually well circumscribed but not encapsulated, and lacks the distinct lobulations of thymoma. It tends to be highly vascularized and may be'frankly hemorrhagic.-

Microscopically, thymic carcinoid tumor exhibits ribbon and festoon formation, rosette-like glands with central lumina, 'balls' of cells with central necrosis and calcification, marked vascularization and frequent lymphatic and blood vessel invasion. Lymphocytes, perivascular spaces, and other features of thymoma are absent. The tumor cells have a more granular cytoplasm than those of thymoma, the nuclear chromatin is slightly coarser, and mitotic activity is frequent.

Carcinoid tumor . Ribbons and rosettes Central necrosis with calcification

IHC lmmunohistochemically,there is reactivity for keratin, chromogranin, synaptophysin, neuronspecific enolase, and other general endocrine markers. In addition,the tumors associated with Cushing syndrome show positivity for adrenocorticotropic hormone (ACTH). Other substances detected in this tumor include serotonin, somatostatin, cholecystokinin,neurotensin. and metenkephalin

Neuroendocrine carcinoma Smal cell n.e.c Large cell n.e.c - indistinguishable from that of its pulmonary counterpart -a mediastinal metastasis of a pulmonary neoplasm has been ruled out. - There are also cases combining features of carcinoid tumor and small cell carcinoma in the same lesion higher number of mitoses (over 10 per 10 HPF) and exhibit foci of necrosis, often extensive. In general, their neuroendocrine architecture is not nearly as well developed. It is manifested - at most - by nesting with peripheral palisading and some rosette-like structures.

NOT ALL MEDIASTINAL NEUROENDOCRINE CARCINOMAS ARE FROM THYMIC ORIGIN NOT ALL THYMIC TUMORS WITH NEURAL DIFFERENTIATION ARE NEUROENDOCRINE CARCINOMA NOT ALL MEDIASTINAL NEUROENDOCRINE CARCINOMAS ARE FROM THYMIC ORIGIN

IHC OF THYMIC CARCINOMA 1-CD5 POSITIVE 2-CD117 POSITIVE 80-86% 3-CD70 POSITIVE 4-TTF1 NEGATIVE 5-P53 and BCL2 stronger than thymomas 6-focal neuroendocrine differentiation

Well circumscribed tumors are often cured by local excision Thymic carcinoid is a more aggressive neoplasm than bronchial carcinoid

sternberg

Immunohistochemically, TCTs are regularly reactive for keratin, neuron-specific ()'-dimeric) enolase, synaptophysin, CD56, CD57, and chromogranin A

Immunohistochemically, the nonepithelial nature of paragangliomas is reflected in their consistent negativity for keratin and EMA. Instead, these neoplasms express neurofilament protein or vimentin (410). The S-100 protein immunostain may be employed to decorate fusiform "sustentacular" cells that surround cellular nests in paragangliomas (442), and the tumor cells themselves often contain one ofthe enkephalin neuropeptides