You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Outcome", "Participant", "Intervention"].

Please return the output as a JSON object of the format: {"Participant" : ["patients with COPD", ...], "Intervention" : ["Atenolol", ...], "Outcome" : ["blood pressure", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Randomized trial of fenretinide in superficial bladder cancer using DNA flow cytometry as an intermediate end point . Retinoids have shown a potential activity in preventing tumor recurrence in superficial bladder cancer . We assessed the activity of the synthetic retinoid fenretinide in superficial bladder cancer using DNA flow cytometry and conventional cytology as surrogate biomarkers . A total of 99 subjects with resected superficial bladder cancer ( pTa , pT1 ) were randomized to either fenretinide ( 200 mg day p.o . for 24 months ) or no intervention . Cystoscopy and bladder washing for DNA flow cytometry end points ( proportion of DNA aneuploid histograms , hyperdiploid fraction , and percentage of apoptotic cells ) and proportion of abnormal cytological examinations were repeated every 4 months for up to 36 months . The primary study end point was the proportion of DNA aneuploid histograms after 12 months . This figure was 48.9 % in the fenretinide arm and 41.9 % in the control arm ( odds ratio , 1.16 ; 95 % confidence interval , 0.44-3.07 ) . There was no difference in any other response biomarker between the two groups up to 36 months , nor was any biomarker able to predict recurrence risk . Recurrence-free survival was comparable between the arms ( 27 events in the fenretinide arm versus 21 in the control arm ; P = 0.36 ) . Twelve subjects in the fenretinide arm complained of diminished dark adaptability , and nine subjects in the fenretinide arm versus one control subject had mild dermatological alterations . We conclude that fenretinide showed a lack of effect on the DNA content distribution and the morphology of urothelial cells obtained in serial bladder washings . Recurrence-free survival was comparable between groups . Because our data are hampered by the lack of predictivity of the selected biomarkers , additional studies are necessary to assess the activity of fenretinide in preventing bladder cancer .
{"Intervention": ["fenretinide", "no intervention", "synthetic retinoid fenretinide", "fenretinide ( 200 mg day p.o ."], "Outcome": ["morphology of urothelial cells", "abnormal cytological examinations", "dark adaptability", "proportion of DNA aneuploid histograms", "Recurrence-free survival", "mild dermatological alterations", "content distribution", "response biomarker"], "Participant": ["superficial bladder cancer"]}