CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
Sinchita Roy-Chowdhuri, MD, PhD
May 2019—The genomic landscape of non-small cell lung carcinoma is evolving constantly with the discovery of a growing number of molecular alterations and associated targeted therapies that have an impact on patient care. The CAP, International Association for the Study of Lung Cancer, and Association for Molecular Pathology issued a guideline in 2013 to provide a road map for molecular testing to select patients for treatment with targeted tyrosine kinase inhibitors.1 The guideline was updated in 2018 and endorsed by the American Society of Clinical Oncology. It provides recommendations that affect cytopathology and the role of the cytopathologist in providing clinically relevant genomic information for the treatment of patients with NSCLC.2,3
The main updated recommendations pertaining to cytologic specimens are summarized in Table 1. One is the endorsement of “any cytology sample with adequate cellularity and preservation” for molecular testing. This is a significant update from the 2013 guideline in which cell blocks were recommended as a preferred substrate for testing. The updated guideline opens the door to better utilization of non-cell block (i.e. non-formalin-fixed, paraffin-embedded cytology) preparations such as direct smears, cytospin preparations, touch preparations, and liquid-based cytology. Several studies have indicated the limitations of restricting molecular testing to cell blocks alone, including a lack of on-site assessment for adequacy, variable cellularity, and suboptimal nucleic acid quality subject to formalin fixation and paraffin embedding.4-6 To this effect, multiple institutions have validated non-FFPE cytology substrates for molecular testing and have shown in some instances that it may provide a superior substrate than their FFPE counterparts.7-10 This may be due in part to the absence of cross-linking formalin artifacts in non-FFPE cytologic preparations resulting in the retrieval of better quality nucleic acids.
ASCO’s endorsement of the 2018 guideline mentions the use of direct smears as the cytologic specimen of choice for lung cancer molecular testing.3 One significant advantage of direct smears over other specimen preparations is the ability to perform rapid on-site evaluation for adequacy assessment, leading to adjustments in specimen collection and appropriate triage to ensure testing success. Dedicated smears and/or touch preparations (in cases with core biopsies) can be sequestered for molecular testing at the time of the procedure, thus reducing turnaround time and additional processing of slides.11 However, any change in the current workflow in the majority of laboratories that are not equipped for the use of non-FFPE cytology preparations for molecular testing will require communication and coordination with significant infrastructure support. In addition, molecular laboratories must be willing to perform the necessary validation for non-FFPE material to allow for testing of cytology preparations.4 Notwithstanding, the importance of this change in the updated 2018 guideline cannot be overstated because it will likely allow for testing in patients who otherwise may not have adequate tumor on FFPE material.
While the 2013 guideline acknowledged the potential of next-generation sequencing as a promising option for simultaneous detection of multiple targetable molecular alterations, the data at that time were insufficient to recommend NGS implementation in a clinical setting. Since then, however, numerous studies have outlined the feasibility and utility of high-sensitivity, high-throughput, and multi-gene assays for interrogating NSCLC for comprehensive genomic profiling. The ability to detect multiple molecular alterations from small amounts of nucleic acids in a single NGS assay led to the revised recommendation in 2018 that says “multiplexed genetic sequencing panels are preferred over multiple single-gene tests.” Several studies using cytologic material including cell blocks as well as non-FFPE substrates have shown them to be equally effective in genomic profiling of NSCLC by NGS analysis.9,12-18 In fact, some studies have indicated better quality metrics when comparing NGS analysis in non-FFPE cytologic substrates versus FFPE material.7,19