1. The document discusses immunohistochemical diagnosis of carcinoma from an unknown primary site. Certain transcription factors and keratins can help identify the organ of origin for metastatic cancers of unknown primary. 2. Transcription factors like TTF1, CDX2, GATA3, NKX3-1, PAX8 are highly specific markers that can identify lung, colon, breast, prostate, and thyroid primary cancers, respectively. 3. Combinations of markers like CK7+/CK20+ suggest origins in organs like the bladder, pancreas, or upper GI tract. The document reviews expression patterns of various markers to diagnose primary organ site in cancer of unknown primary.