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Based on the principle of synthetic lethality , PARP inhibitors have been shown to be very effective in killing cells deficient in homologous recombination ( HR ) , such as those bearing mutations in BRCA1 / 2 .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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