Early Cancer Detection in Asymptomatic Subjects through Measurement of Crosslinked cf-Nucleosomes in Plasma

Purpose: Plasma cell-free nucleosome (cf-nucleosome) measurements are used in veterinary, but not human medicine, to identify asymptomatic subjects at high risk of cancer. Uniquely among plasma sandwich immunoassay tests, cf-nucleosomes are nucleoproteins with a complex electrochemistry. Formaldehyde crosslinking is common in the investigation of cellular nucleoproteins by chromatin immunoprecipitation. cf-nucleosome sandwich immunoassay similarly involves isolation from plasma by chromatin immunoprecipitation. We investigated immunoassay of crosslinked plasma cf-nucleosomes in human cancer samples. Experimental Design: Plasma cf-nucleosomes were covalently crosslinked by blood collection in tubes containing a formaldehyde-releasing agent. Plasma samples were collected from asymptomatic healthy volunteers, treatment-naive cancer patients diagnosed with one of 21 different cancer types, and hospitalized patients with non-cancer conditions. Samples were assayed for a variety of nucleosome species at two independent sites and using immunoassays available from different commercial manufacturers. The assay cutoff was set at the highest cf-nucleosome level measured for any asymptomatic control subject to obtain results for cancer patients at 100% observed specificity.Results: An elevated level of crosslinked plasma cf-nucleosomes was observed in 112 of 229 cancer patients tested (49% sensitivity), including 11 of 32 Stage I solid cancers (34% Stage I sensitivity). Elevated levels also occurred in hospitalized patients with non-cancer pathologies, but no false-positive results occurred among 150 asymptomatic control subjects. Conclusions: Immunoassay of crosslinked plasma cf-nucleosomes achieved clinically meaningful sensitivity for cancer at 100% observed specificity in asymptomatic subjects, and shows promise for the identification of asymptomatic individuals at high risk of an undetected cancer.