While it is obvious from our data that a positive FABP1 immunostaining in a metastatic tissue of unknown origin would pinpoint towards the liver or the gastrointestinal tract as the most likely sites of cancer origin, the highest diagnostic utility may be derived from the constant absence of FABP1 immunostaining in 169 analyzed adenocarcinomas of the lung. The gene discussed is FABP1; the disease is adenocarcinoma.