This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Estrogen receptor studies in carcinoma breast is done on- 
Select and explain. 
A. Blood, B. Urine, C. Tumour tissue, D. Ovary
C: Tumour tissue
Answer: C: Tumour tissue 
Explanation: None