Maximizing Cytologic Specimen Supernatants: A New Player in the Molecular Toolbox

Multiple cytologic preparations are available to cytopathologists to use for molecular testing (MT). Proper use of each is necessary to improve patient outcomes. Residual cytology specimens and cytology specimen supernatants (CSSs) are novel sources from which nucleic acid may be extracted for MT. CSSs may be of particular interest to the cytology community, as it is routinely discarded. If repurposed for MT instead, it may allow pathologists to preserve cellular material from traditional preparations for other ancillary studies.

To evaluate the utility of CSS, it is first necessary to understand the metrics by which MT is evaluated. These include nucleic acid quantity and tumor percentage, the latter of which may be difficult to precisely quantify in CSS. Metrics of nucleic acid quantity include direct measures, such as degradation value (measure of nucleic acid fragmentation), and indirect measures, including many sequencing-derived metrics and concordance with formalin-fixed, paraffin-embedded tissue or cell blocks. Specimen contamination and turnaround time (TAT) are also critical for patient care. Human papillomavirus testing on residual cytology specimens serves as a model of the clinical utility of MT. More recently, studies have examined both the analytic and clinical value of a broad range of MTs performed on CSS derived from both exfoliative and fine needle aspiration cytology specimens and from specimens collected with and without fixative. These studies have demonstrated that CSS contains both cellular (genomic) and cell-free nucleic acid and that its great advantages lie in reductions in specimen contamination and improvements in TAT. Variations in nucleic acid quantity and quality among studies suggest that further specimen optimization is desirable as CSS becomes more widely adopted as a source of nucleic acid.

CSSs are no longer considered "waste" material. When handled properly, they can complement conventional cytomorphology and expand the role of cytopathology in precision medicine. Until CSSs are fully validated, the information derived from them should be integrated with other findings.