Characteristics of Exceptional or Super Responders to Cancer Drugs

To summarize case reports of exceptional and super responders already published in the biomedical literature.

We searched for published case reports or abstracts of exceptional or super responders to a cancer drug using PubMed and Google Scholar search engines. Pooling such reports is widely considered a promising research strategy and the subject of several ongoing investigations, including the National Cancer Institute's Exceptional Responders Initiative. All articles were read in full, including relevant references. We extracted clinical characteristics of exceptional or super responders, including age, tumor type, drug, genetic mutations, depth of response, duration of response, number of previous lines of therapy, duration of response to a previous line of therapy, and the number of patients treated similarly to identify the exceptional case. This study was performed between March 1, 2015, and April 30, 2015.

Among 489 articles, 32 exceptional responders were identified. The most common malignancies described were renal cell cancer (5 of 32 [16%]) and urothelial carcinoma (4 of 32 [13%]). The use of targeted agents was common in these cases (26 of 32 [81%]), particularly inhibitors of the mTOR pathway (16 of 32 [50%]). The median duration of response among responders was 17.5 months, and 59% (19 of 32) of the patients were last known to be alive with continuing response or stable disease. Notably, 46% (12 of 26) of the patients had received 2 or more previous lines of therapy and 6 of the 32 cases (19%) did not report this information. Few authors report the number of patients treated similarly to observe the super response (12 of 32 [38%]).

Exceptional or super responders to cancer drugs have been described in the literature; however, there is incompleteness in the reporting of relevant data that may help clarify whether such responses are secondary to treatment or reflect underlying biology.