
Extract the answer to the question from the following context.
Question: What does a dog have to do to be able to start detecting cancer?
Context: Medical detection dogs are capable of detecting diseases by sniffing a person directly or samples of urine or other specimens. Dogs can detect odour in one part per trillion, as their brain's olfactory cortex is (relative to total brain size) 40 times larger than humans. Dogs may have as many as 300 million odour receptors in their nose, while humans may have only 5 million. Each dog is trained specifically for the detection of single disease from the blood glucose level indicative to diabetes to cancer. To train a cancer dog requires 6 months. A Labrador Retriever called Daisy has detected 551 cancer patients with an accuracy of 93 percent and received the Blue Cross (for pets) Medal for her life-saving skills.

train
