BRCA1 and neoplasm: This lack of information is due to many factors including: (1) the size of the BRCA1 protein (~208 kDa) makes it difficult to express recombinantly; (2) the inherent flexibility of full-length BRCA1 renders it problematic to crystallize; and (3) few strategies are available to isolate BRCA1 protein assemblies from human tumor cells for structural analysis.