ERBB2 and neoplasm: Based on both the low frequency of ERBB2 amplification in the original tumor and the OCI-C5x parental cell line, we propose that acquisition of ERBB2 amplification is a late event in the primary ovarian-localized tumor, generating a small subpopulation of cells with elevated ERBB2 expression which strongly enhances anchorage independence, thus promoting survival and proliferation of tumor cells shed into the peritoneum.