The Pap smear, pioneered by Dr. George Papanicolaou and his wife Andromache, represented the greatest cancer screening and prevention program in human history — but it wasn’t without limitations. More recently, it has been replaced by what we call liquid-based cytology (LBC) Pap tests that don’t require “smears” at all. But a change in name — from Pap smear to Pap test — is just the beginning of the advances this evolution represents, as covered in an excellent recent article. As the assistant medical director and director of clinical pathology at PathAdvantage, the lab that processes all of your MyPathAdvantage tests, I agree with this article’s assessments.
The Rise and Fall of the Pap Smear
Starting with its widespread adoption in the 1970s, the Pap smear brought with it a vast advance in cervical cancer prevention. Its effectiveness in reducing the deadly effects of cervical cancer is undeniable, in countries with national screening programs.
However, the conventional Pap smear faced criticism, mostly for issues with false negatives — women with precancerous or cancerous cells that were not identified by the test. Additionally, interpreting Pap smears was a labor-intensive task and required extensive training of pathologists. Although the Pap smear represented an amazingly successful cancer screening program, many questioned how the test might be improved.
In the 1990s, a new approach, Liquid Based Cytology (LBC) Pap tests, emerged as a potential advancement from the Pap smear. It introduced a new approach to cervical cell collection and analysis.
The conventional Pap test is collected in the following manner: Cells are gently scraped from the cervix with a spatula and literally smeared onto a glass slide for microscopic evaluation — thus the name Pap smear. Conversely, LBC utilizes a special brush to collect a sample of cervical cells. These cells are removed from the brush via rinsing with a liquid medium. This liquid sample is then sent to a laboratory for processing.
Our Perspective On LBC Pap Test Advantages
LBC offers several advantages over the Pap smear. Our laboratory has processed both types of Pap tests for more than two decades, and we agree with the article’s assessment:
- Standardized Sample Collection: The LBC brush collection technique ensures a more consistent and representative sample of cervical cells compared to the variability that can occur with conventional Pap smears. Conventional Pap smears can result in samples that are wildly different in quality depending on the technique used to create the smear. With LBC, the sample can be more consistent and representative because of the automation involved.
- Improved Sample Quality: The liquid medium in LBC helps to preserve the cells. This leads to clearer and easier interpretation for cytopathologists — pathologists that examine cells to diagnose diseases. The liquid medium also prevents what we call “artifacts” on the slide which can make microscopic evaluation of the cells more challenging. Artifacts common on conventional Pap tests include:
- Cell drying, which causes the cells and nuclei to enlarge, or the cells to crack. This doesn’t occur with LBC, because the cells are contained in a preserving medium.
- Extreme cellular thickness. Because individuals smear the cells on a slide, they can leave thick layers of cells. This makes the evaluation of individual cells very difficult or impossible. In LBC, the cells are processed and dispersed evenly in a single layer, or ‘monolayer, making cellular thickness much more infrequent.
- Obscuring blood or mucus can be removed via filtration during the LBC process.
- Fewer “unsatisfactory” Pap tests: This prevents the need for a repeat patient visit and recollection. For example, a conventional Pap test requires 8,000-12,000 cells for it to be considered adequate; a LBC Pap test requires only 5,000 cells for adequacy, per the Bethesda cytology system for reporting cervical cytology.
- Increased Detection Rates: Studies have shown that LBC may improve the detection rate of precancerous cells and even early cervical cancer compared to conventional Pap smears.
- HPV Testing Potential: The liquid sample from LBC can be used for human papillomavirus (HPV) testing, a crucial factor in cervical cancer risk assessment. Patients with unclear results must undergo additional testing to determine if they have HPV. If HPV is negative, the patient, pathologist, and Ob/Gyn can rest easy. The odds of developing cervical cancer in the absence of an HPV infection are slim. However, if a conventional Pap smear is received, there is no additional material with which to perform an HPV test, and this necessitates either an uncomfortable colposcopy, or a repeat visit to collect further samples for HPV testing. Patients with LBC Pap tests do not need a repeat visit for additional testing, since that testing can be completed with the LBC test sample.
- Automation: The liquid-based format of LBC samples allows for greater automation in processing and analysis, potentially leading to increased efficiency and consistency in the future.
While there are many positives to LBC, it’s important to acknowledge the following:
- Cost-effectiveness: LBC is slightly more expensive than Conventional Pap smears, but are more cost-effective overall, especially when additional HPV testing is required.
- Further triage: Sometimes, additional testing methods are required beyond the LBC and HPV tests (such as HPV genotyping, FISH testing or other more advanced/specialized molecular forms of triage). The guidelines that define the need for further workup or colposcopy are constantly undergoing refinement and are usually reported/recommended by organizations such as ACOG (the American College of Obstetricians and Gynecologists) or ASCCP (the American Society for Colposcopy and Cervical Pathology.)
- Automation and Standardization: Automation in LBC processing holds promise for increased efficiency and consistency, but it requires research, development, validation and implementation. Still, a new automated artificial intelligence system (GeniusTM) was recently FDA-approved and demonstrates the possibilities. The GeniusTM system adds additional LBC slide screening and uses AI that screens the slide before the cytotechnologist and pathologist look at it, highlighting areas of the slide and individual cells of concern.
Many of our patients have undergone conventional Pap smears and modern LBC Pap tests. As a pathologist, the LBC Pap Tests mark a significant advancement in cervical cancer screening and in women’s healthcare overall. Our laboratory, founded by a leading woman pathologist, has been dedicated to improving women’s healthcare for two decades. LBC will likely continue to play a crucial role as medicine evolves, becoming more refined and effective overall.
