A comprehensive review of exceptional responders to anticancer drugs in the biomedical literature

Abstract

Importance: There is broad interest in patients who have exceptional responses to cancer drugs and only one prior systematic review of published case reports.

Objective: To systematically summarise case reports of patients who have had a super response to a cancer drug and determine patterns and completeness of documentation.

Design, setting and participants: This is a systematic search of biomedical literature and hand searches of seven prominent oncology journals. All cases were adults with cancer in the metastatic or unresectable setting and who were classified as having a remarkable response to a drug therapy were included. Our study was conducted between January 2017 and April 2017.

Main outcomes and measures: We extracted patient and tumour characteristics, characteristics surrounding the exceptional response and pertinent oncologic history. Additionally, we noted authors' financial conflicts of interest, if given.

Results: We found 180 cases of exceptional response. The most common malignancy was breast cancer (28/180), and the most common class of drug therapy used was targeted therapies (161/274). The median year of publication was 2015. Depth of response included 33% (61/180) complete response, 55% (100/180) partial response and 7.7% (14/180) stable disease. The median length of response to the drug was 14 months. Fifty-nine percent (107/180) reported a driver mutation, and only 52% (56/107) reported two or more correlative studies. Only 14% (26/180) reported a denominator or total number treated to observe this response. Of cases that reported duration of response to a previous drug given in the unresectable setting, 49% demonstrated a progression-free survival ratio of exceptional response to prior line of 1.3 or greater (Von Hoff ratio).

Conclusions and relevance: Our survey found that exceptional responders tended to have solid organ malignancies and most received targeted therapies. Many of our cases of exceptional responders were missing important information about the response and key oncologic history. Standardised criteria should be used to maximise usefulness of these case reports in the future.

Keywords: Cancer outliers; Dramatic response; Exceptional responders; Super responders; n of 1 medicine.