Rucaparib camsylate (CO-338; 
8-fluoro-2-{4-[(methylamino)methyl]phenyl}-1,3,4,5-tetrahydro-6H-azepino[5,4,3-cd]indol-6-one 
((1S,4R)-7,7-dimethyl-2-oxobicyclo[2.2.1]hept-1-yl)methanesulfonic acid salt) is 
a PARP1, 2 and 3 inhibitor. Phase I studies identified a recommended Phase II 
dose of 600 mg orally twice daily. ARIEL2 Part 1 established a tumor genomic 
profiling test for homologous recombination loss of heterozygosity 
quantification using a next-generation sequencing companion diagnostic (CDx). 
Rucaparib received US FDA Breakthrough Therapy designation for treatment of 
platinum-sensitive BRCA-mutated advanced ovarian cancer patients who received 
greater than two lines of platinum-based therapy. Comparable to rucaparib 
development, other PARP inhibitors, such as olaparib, niraparib, veliparib and 
talazoparib, are developing CDx tests for targeted therapy. PARP inhibitor 
clinical trials and CDx assays are discussed in this review, as are potential 
PARP inhibitor combination therapies and likely resistance mechanisms.