From Exfoliative Cytology to Oral Brush Biopsy: An Advance in the Early Detection of Oral Precancers and Cancers
The high mortality rate from oral cancer is due to several factors, but undoubtedly, the most significant is delayed diagnosis. Studies have demonstrated that the survival and cure rate dramatically increase when oral cancer is detected in its precancerous stage or at an early asymptomatic stage. For example, the 5-year survival for patients with localized disease approximates 80% compared to 20% for those with distant metastases. Unfortunately, approximately two thirds of patients at time of diagnosis are symptomatic, and over 50% display evidence of spread to regional lymph nodes and metastases. Given the significant morbidity and mortality associated with advanced oral cancer and its treatment, the need to provide clinicians with an accurate diagnostic technique that will increase the detection of early stage oral cancer has been compelling.
Advances in the early detection of oral cancer are unfolding and analogous to those made in the advances for cervical cancer. In the early 1950's, cervical cancer was the second leading cause of cancer deaths in American women. The disease was diagnosed by biopsy, which was usually triggered by advanced symptoms such as persistent spotting and bleeding. Cervical cancer, like oral cancer, is highly curable when detected at an early dysplastic stage and highly morbid when detected at a late, symptomatic stage. By the late 1960's, cervical cancer dropped to the seventh leading cause of cancer deaths in American women. The difference was due to the widespread utilization of cytology, specifically, the cervical Papanicolau smear. The routine use of the Pap test has resulted in a reduction of cervical cancer deaths in the United States by 74%.
Cytology has broad potential to fill the "screening
gap" which currently challenges the early detection
of many epithelial cancers, including oral cancer. That
is, cytology can be an effective and noninvasive means
of detecting dysplasia and early carcinoma in those patients
who are either asymptomatic or in those with minor symptoms
who do not warrant immediate biopsy. The mechanism of cytology,
regardless of its application to cervical, bladder or oral
mucosal lining, is based upon the fact that dysplastic
and cancerous cells tend to have fewer and weaker connections
to each other and to their neighboring normal cells in
the surrounding tissue. Dysplastic and cancerous cells
therefore, tend to "slough off" or exfoliate
preferentially and can easily be collected from the surface
of the lesion. A sample of these cells applied to a microscope
slide will often contain abnormalities if harvested from
a dysplastic or cancerous lesion.
The success of the Pap smear was a primary impetus for a large number of studies conducted in the mid1960's examining the sensitivity and specificity of oral exfoliative cytology. Exfoliative cytology was thought of as a technique that could facilitate and accelerate clinical and histopathologic recognition of oral cancer. The use of oral cytology for large, advanced and obviously malignant lesions is limited since such growths always require a definitive biopsy-obtained diagnosis. In contrast, the value of cytology lies in the identification of early stage oral cancers and dysplasias whose clinical appearance is often innocuous or trivial. The use of oral cytology has been shown to accelerate biopsy of these clinically harmless-appearing cancers that would have otherwise been neglected. Furthermore, oral cytology has been demonstrated repeatedly to reveal carcinoma in patients whose initial noncancerous diagnosis was based upon false negative biopsy results.
Despite the initial high degree of interest and research, traditional, manual oral cytology currently is not utilized as a method of diagnosing oral precancers and cancers. Although many authors initially concluded from their data that oral cytology could serve as a useful adjunct to biopsy, the current general perception among both dentists and physicians is that the sensitivity of oral cytology is not sufficient to warrant its widespread use as a screening modality to triage visible lesions.
There are several reasons why traditional oral cytology has proven to be of little value in detecting oral dysplasias and cancers. When cytologic instruments are used in the mouth to diagnose precancers and cancers, their accuracy is relatively low. Specifically, exfoliative cytology performed on oral cancers has high false negative rates, which can exceed 30%. Furthermore, the effectiveness of exfoliative cytology for detecting dysplasia is even more doubtful, with false negative rates reported as high as 63%.
These poor results are due, in part, to the fact that cytology instruments do not sample the deepest layers of the oral lesion. This is essential, since unlike cervical cancer, the deepest layer of the lesion, the basal cell layer, is often the only layer that contains abnormal cells within an oral precancerous or cancerous lesion. Furthermore, since the sensitivity of cytology is often dependent on a tedious visual search for a potentially rare abnormality on the microscope slide, the precancerous or cancerous cells collected on the slide may not have been detected by the laboratory pathologist. This results from the fact that although abnormal cells may preferentially exfoliate from a dysplastic lesion, they are often vastly outnumbered on the microscope slide by the enormous numbers of normal cells that exfoliate due to constant turnover. For example, a cervical Pap smear from a patient with carcinoma-in-situ may contain 300,000 normal cells with only a dozen abnormal cells scattered among them. Several recent studies have demonstrated that women who develop advanced cervical cancer despite a history of "negative" Pap smears often experienced one or more false negative smears determined as such because they contained very few abnormal cells. In oral cytology, this false negative dilemma is exacerbated by two additional factors: 1) the number of abnormal cells available for sampling may be limited by the keratinized nature of many oral lesions and, 2) the high rate of epithelial turnover in the mouth may further numerically dilute the few abnormal cells obtained in the smear.
For cervical cancer, the false negative problem inherent in cytological screening has not deterred the use of the Pap smear, but has resulted in efforts to improve its sensitivity through the use of improved sampling methodology and improved computer assisted inspection of the slide.
The oral brush biopsy was introduced to the dental profession in 1999, overcoming the limitations of traditional oral cytology. This biopsy method utilizes a brush to obtain a complete transepithelial biopsy specimen with cellular representation from each of the three layers of the lesion: the basal, intermediate, and superficial layers. Unlike cytology instruments, which collect only exfoliated superficial cells, the biopsy brush penetrates to the basement membrane, removing tissue from all three epithelial layers of the oral mucosa. The oral brush biopsy does not require topical or local anesthetic and causes minimal or no bleeding or pain. The brush biopsy instrument has two cutting surfaces, the flat end of the brush and the circular border of the brush. Either surface may be used to obtain the specimen.. In a recent study, paired, same-site samples of tongue tissue were obtained from patients, first by brush biopsy and then by surgical punch biopsy. The study demonstrated that the brush biopsy technique, unlike cytology, sampled the full thickness of oral epithelium and obtained epithelial cells similar in representation to surgical 6 mm punch biopsy specimens.
Brush biopsies are utilized routinely in the detection of precancer and cancer in other organ systems. Examples of well-known applications of brush biopsies include fiberoptic bronchoscopy (bronchial), ureteral retrograde brush biopsy (renal or ureter tissue), cholangiography (bile duct stricture), pancreatic ductal brush biopsies and others, including endometrial, nasopharynx, and GI tract applications (rectal, gastric, esophageal, colon). Their use in the oral cavity has only recently been introduced as OralCDx testing.
The improved accuracy of the OralCDx brush biopsy over traditional manual cytology is due, in part, to the fact that the entire thickness of the lesion is sampled- cells from all layers are collected. Furthermore, the analysis of the specimens is aided with a highly specialized neural network-based image processing system specifically designed to detect oral precancerous and cancerous cells, detecting as few as one or two abnormal cells scattered among tens of thousands of normal cells. The core technology behind the OralCDx computer was originally developed for the missile defense system. Without the computer-assisted analysis, the abnormal cells are often overlooked with just manual inspection. The patented brush biopsy tool, which samples all of the layers of the lesion, together with analysis of oral brush biopsies assisted with sophisticated computers make the OralCDx test highly accurate. In two independent studies, the first conducted in the U.S. at 35 academic dental centers whose results were published as the cover story in the Journal of the American Dental Association, and the second, at a prestigious German university, OralCDx was shown to have a sensitivity of greater than 95% and a specificity over 90%.
One major problem inherent in current oral cancer screening is that by visual examination alone, precancers and early stage oral cancers cannot be adequately identified, and such lesions may easily be overlooked and neglected, even by highly trained professionals. It is well established that oral lesions which appear innocuous may occasionally harbor dysplasia or cancer and that a delay in diagnosis may limit treatment options, ultimately resulting in a poor prognosis for the patient. Not uncommonly, patients fail to return in a timely fashion for follow-up visual examination of a lesion which the practitioner believes is minimally questionable.
Until recently, the only method of diagnosing an oral cancer or precancer was to biopsy a suspicious lesion by traditional methods. The diagnosis of an oral cancer is, accordingly, made when an oral lesion is suspicious enough that it causes the dentist to refer the lesion for biopsy. For example, clinical features and symptoms of a suspicious lesion include large size, ulceration, and pain, and although these are all indications for immediate biopsy, an oral cancer that exhibits any of these features, all too often, is already considered advanced.
The results of brush biopsy studies demonstrate that the
tool can be reliably utilized on oral lesions as a method
of confirming their benign nature and more importantly,
revealing those that are precancerous and cancerous when
they are not clinically suspected. The role for OralCDx
is to help determine the true nature of lesions which would
not otherwise receive any further testing, i.e. lesions
which are not judged to be sufficiently suspicious on visual
inspection to be referred for immediate biopsy.. Thus,
the brush biopsy is a method of detecting a precancerous
lesion, which can prevent oral cancer from ever developing,
and it is a method of identifying unsuspected oral cancers
at early and curable stages.
The brush biopsy provides dentists with a diagnostic screening test similar to a Pap smear. Whereas the Pap smear is a procedure performed on all women and a brush biopsy is used only in patients with a visible mucosal spot, both tests are adjuncts to the clinical examination and are used to identify a disease at an early and curable stage, when it is unsuspected; both are simple to perform, office-based, painless tests; both procedures have been integrated into the daily routine of practice; both have saved thousands of lives. Given the difficulty in clinically differentiating premalignant and early malignant oral lesions from those that are benign, the brush biopsy allows practitioners to test lesions that are encountered daily, thereby eliminating a barrier that has hindered the detection of early, curable oral cancers. For the population who visit their dentists routinely, the opportunity to improve the poor survival rate and morbidity of oral cancer through early diagnosis is now attainable.