This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Clinical Aspects of Neoplasia, Subject name: Pathology
Which of the following carcinoma most frequently metastasizes to brain - 
Select and explain. 
A. Small cell carcinoma lung, B. Prostate cancer, C. Rectal carcinoma, D. Endometrial cancer
A: Small cell carcinoma lung
Answer: A: Small cell carcinoma lung 
Explanation: Ans. is 'a' i.e., Small cell carcinoma of lung Frequency of Nervous system metastasis by common primary tumour. Site of primary tumourBrain %MetastasesLeptomeningeal % MetastasisSpinal cord % CompressionLung402418Breast194124Melanoma10124Gastrointestinal tract7136Genitourinary tract7-18Others171030