Complex sentence: Some studies of cancers report over-expressed "BRCA2", other studies report under-expression of "BRCA2", and at least two reports found over-expression in some sporadic breast tumors and under-expression in other sporadic breast tumors.
Split into simpler sentences: Some studies of cancers report over-expressed "BRCA2" whereas other studies report under-expression of "BRCA2". At least two reports found over-expression in some sporadic breast tumors and under-expression in other sporadic breast tumors.