why is it that some respond well and many others do not?

Patients will dramatic and long-lasting respone to treatment that was not effective for most similar patients are considered exceptional responders.

Who is an Exceptional Responder?
An exceptional responder is defined as a patient with cancer who has:

a complete response to a drug(s) where complete response is seen in less than 10% of patients receiving similar treatment; or
a partial response lasting at least 6 months where such a response is seen in less than 10% of patients receiving similar treatment; or
a complete or partial response that lasts longer than 3 times the median response duration in the literature for the treatment

Read more: https://www.cancer.gov/news-events/cancer-currents-blog/2017/exceptional-responders-progress?cid=eb_govdel

The National Cancer Institute (NCI) has embarked on the Exceptional Responders Initiative (ERI) to understand the molecular underpinnings of exceptional responses to treatment, primarily via chemotherapy, in cancer patients.

To read more: https://www.cancer.gov/about-cancer/treatment/research/exceptional-responders-initiative-qa

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