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
Bilaterality with medullary carcinoma of breast is seen in: 
Select and explain. 
A. < 5%, B. 10%, C. 20%, D. 50%
C: 20%
Answer: C: 20% 
Explanation: Medullary carcinoma is a special-type breast cancer; it accounts for 4% of all invasive breast cancers and is a frequent phenotype of BRCA1 hereditary breast cancer. Grossly, the cancer is soft and hemorrhagic. A rapid increase in size may occur secondary to necrosis and hemorrhage. On physical examination, it is bulky and often positioned deep within the breast. Bilaterality is repoed in 20% of cases. Ref: Schwaz's principle of surgery 9th edition, chapter 17.