Arjun Nair MBCHB, FRCR, Presenter: Nothing to Disclose

Brendan Tinwell MBBS, Abstract Co-Author: Nothing to Disclose

John Du Parcq MBBS, Abstract Co-Author: Nothing to Disclose

Sisa Grubnic MD, Abstract Co-Author: Nothing to Disclose

Anand Devaraj MBBS, Abstract Co-Author: Nothing to Disclose

Ioannis Vlahos MBBS, Abstract Co-Author: Researcher, Siemens AG Consultant, Siemens AG Consultant, General Electric Company Consultant, Medicsight, Inc

Praveen Pissay Gopala Rao MBBS, FRCR, Abstract Co-Author: Nothing to Disclose

The origin of tumors found in the thorax, whether primary or metastatic, can be difficult to ascertain. We aim to: Describe the panels of IHC markers used to aid standard histopathological techniques. Illustrate, with examples,how such markers in combination with radiological appearances can help in determining tumor origin.

IHC panels for primary lung tumors ( e.g. p63, TTF1, CK5/6, CK7, etc. to distinguish adeno-; from squamous cell carcinoma) IHC markers to identify metastatic lung lesions e.g. RCC Ma for renal cell carcinoma; initial lymphoma panel e.g. B-cell (CD20) and T-cell (CD3) antigens; HMB-45 for melanocytic lineage Sample size considerations: FNAC vs large gauge biopsy IHC-radiological correlation to distinguish intra- vs extrathoracic origin Treatment implications e.g. targeted chemotherapy

The main teaching points are: IHC panels offer complementary diagnostic utility in defining lung tumor origin in certain situations, especially when cells lack morphological differentiation Increasingly cellular-specific chemotherapy makes tumor origin determination essential; various IHC panels correlated with imaging appearances can achieve greater diagnostic confidence when dilemmas arise. Radiologists who are aware of the spectrum of such panels can offer more informed interpretation.

Nair, A, Tinwell, B, Du Parcq, J, Grubnic, S, Devaraj, A, Vlahos, I, Pissay Gopala Rao, P, A Primer of Immunohistochemical (IHC) Markers in Thoracic Malignancy: Understanding Your Cytopathologist.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015979.html