33 yrs old female underwent excisional biopsy from large nonresectable mediastinal mass with slight compression symtoms (cough). At the time of diagnosis multiple bilateral pulmonary mts were detected. 2 nodes removed with reactive changes. Platinum based chemo is planned. The surgeons mentioned an impression of very fast growth of the tumor.  
HISTO: Undifferentiated large cell nests with "discordant" and prominent ekstracellular keratinisation.  
IH: p63(+++)100%; CD5(-); CK5(+/++) 30% ; PanCK(++) 100% CD30(-); P16(-); CD34(-); PLAP(-); CD117(+/-)(faint) 20%; CEA(-); Ki67 ~60%.  
 
PROPOSAL: Poorly differentiated (highly keratinised) carcinoma: most probably primary mediastinal carcinoma, asociated with t(15;19) translocation (NUT midline carcinoma).  
DIFFERENTIAL (FISH or IH for NUT is required...): PROBABILITIES, AGE AJUSTED:  
1. Pulmonary (young age; Xray multiple bilobary mts);  
2. Thymic (CK5(-); young age; CD117+ (faint)  
3. Head/neck and cervical (p16(-); clinically CT pending; no symptoms).  
4. Somatic carcinoma from GCT (serum markers are negative; rarity for woman).  
 
Thank you for discussion.