MMOD-16 THE CHALLENGES IN ASSIGNING THE PRIMARY SOURCE OF METASTATIC FOCUS: PATHOLOGY POINT OF VIEW

Metastasis to the central nervous system is the most common cause of brain lesions, mostly in adults and mostly in the posterior fossa. Assigning the primary source of metastasis in a patient as a first presentation/ unknown primary is challenging to the pathologist. The diagnosis, in pathology point of view depends primarily on three factors: tumour morphology, the immunohistochemical expression, and clinical correlation to definitely specify the primary site of the metastasis. Missing one of thses factors may mislead the final diagnosis. The morphology of the metastasis may differ from the primary site as the metastasis may include “only” the tiny aggressive variant in the primary site, leading to mis- directing the pathological investigation. In addition, the immuno-expression is highly overlapping over different pathological entities, not mentioning the lab quality of stain. In cases of complex tumors, only one component of the tumor can metastasis leading to mis-labelling of the tumor entity. In conclusion, precise pathological diagnosis on tumor metastatic focus as a primary diagnosis can not be achieved without minding these factors, which are essential information to be delivered to the assigning pathologist.