Hello. You did not present the text to which this question is related, which makes it impossible for it to be answered. However, I will try to help you in the best possible way.
To answer this question, you will need to identify the main idea of the text, which in this case is a blog post. To identify the main idea, you will need to read the text in question and identify the subject that the text is addressed. This subject is the main idea. In general, the main ideas are exposed in the first paragraphs of the text.
Knowing the main subject you will be able to find out what is the relationship that the term "chemotherapy" has with the subject.
