Exciting new advances in oral cancer diagnosis: avenues to early detection

Approaches to Early Detection of Dysplasia and Oral Cancer

There are two approaches in the early detection of oral dysplasia and cancer: 1) oral cancer screening programs that identify asymptomatic patients with suspicious lesions and 2) employing specific diagnostic tools to identify dysplasia and early oral cancers in asymptomatic patients with an oral abnormality. The benefits and limitations of these approaches will be addressed in this review.

Oral Cancer Screening

Screening for oral cancer implies searching for oral precancerous and cancerous lesions, typically before symptoms occur. A number of established cancer screening programs for a variety of malignancies have been shown to significantly reduce patient morbidity and mortality - including the Pap test for cervical cancer and mammography for breast cancer. However, several publications have demonstrated that oral cancer screening has limited value as a method for detecting precancerous or early cancerous lesions. In the only randomized controlled oral cancer screening trial conducted in India and involving over 130,000 individuals, the authors concluded that visual examination was useful as a method of screening for oral cancer only in high risk cases like chronic smokers or alcoholics [2].

Oral cancer screening is fraught with problems including the fact that approximately 5-15% of the general population may have an oral mucosal lesion. While the majority of these lesions are benign, clinical inspection alone cannot differentiate which lesions are potentially precancerous and cancerous and which ones are benign. The classic clinical presentation of a premalignant lesion or malignancy includes a red spot, white spot or persistent ulcer. However, only a small percentage of these types of lesions are cancerous and an oral examination unfortunately cannot discriminate between lesions that are potentially dangerous from lesions that are benign. A Cochrane review on this subject failed to find any evidence to confirm or refute the usefulness of screening for oral malignancies [3].

Early Diagnosis

Early detection of oral cancer is one of the most efficient ways to reduce the high mortality from this disease. Early detection can minimize the morbidity of the disease and its treatment, which is associated with a severe loss of function, disfigurement, depression and poor quality of life.

However, based upon the National Cancer Institute's SEER program, which collects data on oral cancer, there has been little or no change in the past twenty years in the detection of oral cancers at early stages [4]. Unfortunately, most patients are diagnosed with advanced stage disease.

Early detection therefore necessitates raising awareness in the general public and improving access to oral health services for all segments of the population.

Oral squamous cell carcinoma (OSCC) is almost always preceded by a visible precancerous lesion-dysplasia. As highlighted by the American Dental Association, "Identifying white and red the spots that show dysplasia and removing them before they become cancer has proved to be one of the most effective methods for reducing the incidence and mortality of cancer" [5]. Malignant transformation of dysplasia, which is quite unpredictable, occurs over years - during which time the lesion can be treated, potentially preventing oral cancer from developing. Oral precancerous lesions may also occasionally regress if the healthcare professional motivates the patient to reduce the risk factors including elimination of carcinogens including tobacco and alcohol.

Light-based oral cancer screening aids

VELscope is a handheld device that uses visible light in the 430 nm wavelength in order to cause fluorescent excitation of certain compounds in the tissues. (Figure 1a) With Vizilite, patients' first rinse with acetic acid and then the oral cavity is examined with an illuminated chemiluminescent light stick. (Figure 1b) Microlux is similar to Vizilite and requires the patient first rinse with acetic acid; the oral cavity is then examined with a battery-powered fiberoptic visible light source instead of a chemiluminescent visible light source. Orascoptic DK also requires an acetic acid rinse and uses a three-in-one device that employs a battery-powered handheld light source. Since none of these medical devices is a diagnostic test, the manufacturer of these screening aids do not make any claim that the device is either sensitive or specific to the identification of any type of abnormal oral lesion. Furthermore, as we reported in a prospective study examining the potential benefits of several of these lights, the sensitivity of Vizilite was 0% and the sensitivity of VELscope was also poor-50%. We concluded that the use of ViziLite or VELscope along with a conventional screening examination was not beneficial in identifying dysplasia or cancer and clinicians/and patients could have a false sense of security after obtaining a negative ViziLite or VELscope examination result because potentially large numbers of precancerous and cancerous lesions would be missed by both. Until additional studies are performed, these screening lights should only be used to help identify lesions that may have been overlooked with a conventional oral examination and not for determining whether a lesion is precancerous or cancerous. Only a definitive test examining cells or tissue can determine the biologic behavior of a lesion [6].

Cytological Techniques

During the last few decades, oral cytology has resurfaced as the focus of scientific research. However, in contrast to the sampling of cells of the uterine cervix, analysis of surface epithelial cells of the oral cavity and oropharynx by standard exfoliative cytology has proven unreliable so far. The shape of the oral cavity makes it impossible to examine the complete mucosal surface. Without loss of minimal invasiveness, it was not possible to access the deeper cell layers of the oral cavity with conventional exfoliative cytology[7].

Brush Biopsy

During the 1980s, a brush was introduced for cervical smears in gynecological lesions and was later modified for oral smears too. (Figure 1c) This technique demonstrated better cell spreading on objective slides compared with smears obtained by using the conventional wooden spatula as well as an improvement in the cellular adequacy of the smears. The importance of oral brush biopsy was emphasized in a multicenter study where nearly 5% of clinically benign-appearing oral mucosal lesions were sampled by using this technique and later confirmed by using scalpel biopsy to represent dysplastic epithelial changes or invasive cancer [8].

OralCDx^® (OraCDx Laboratories, Inc. Suffern, NY), the oral brush biopsy with computer assisted analysis, is a diagnostic test that identifies dysplasia in common spots that often have no suspicious clinical features. Unlike exfoliative cytology, the brush biopsy collects cells from the full thickness of the oral epithelium. The brush biopsy is a chair-side, easy to perform, painless test that can be used to evaluate any suspicious lesion including common small white and red oral lesions to rule out dysplasia. Since most oral lesions are benign, most test results are likely to be benign. Approximately 10% of all cases usually turn out to be abnormal. Based upon the findings, the laboratory provides specific guidance on these abnormal cases sometimes recommending scalpel biopsy, retesting or observation.

The accuracy of the brush test has been the subject of many published studies. In every study in which an oral lesion was simultaneously tested with both a brush biopsy and scalpel biopsy, this test has been shown to have a sensitivity and specificity well over 90% [8, 9]. These studies demonstrate that the brush biopsy has a high sensitivity in ruling out the presence of dysplasia and cancer making it a practical way to evaluate lesions without an obvious etiology such as infection of trauma.

Discrepancies of brush test and scalpel biopsy results have been reported anecdotally and have incorrectly been labeled brush "false negatives." Unfortunately these anecdotes been quoted repeatedly in the literature despite the fact that they have no validity at all. These discrepant results were all from cases where the scalpel biopsy was performed months after from the brush biopsy. Within a given oral lesion, dysplasia is multicentric and unless the 2 biopsy samples happen to sample the same part of the dysplastic lesion, the results will be discrepant. Furthermore, the biologic nature of a lesion may change over time as benign lesions may become dysplastic and dysplasia may also regress. Most importantly, the histologic diagnosis of dysplasia is not easily reproduced amongst oral pathologists and therefore a discrepant result between brush biopsy and scalpel biopsy may in fact represent a false negative or false positive scalpel biopsy result. Therefore, when comparisons are made between any 2 biopsy techniques (i.e. brush biopsy vs. scalpel biopsy or scalpel biopsy vs. scalpel biopsy) the only valid studies are those which compare the results of both biopsies performed at the same time and from the same portion of the suspicious lesion.

To help localize the optimal site for brushing an abnormality, Gupta et al combined conventional oral brush biopsy with the application of toluidine blue to localize suspect mucosal areas [10].

Scalpel biopsy

Until now, tissue sampling by scalpel biopsy and subsequent histological examination have been the cornerstone for diagnosing premalignant and malignant oral diseases. Unfortunately, scalpel biopsy has many inherent limitations which health care practitioners need to be aware of. For example, vague histopathological definitions as well as histological misinterpretation resulting in false negatives and false positives should be kept in mind while interpreting the results of scalpel biopsies. An oral biopsy is invasiveand involves both psychological implications for the patient as well as possible often technical difficulties for the health practitioner. When lesions are extensive, the most representative areas must be selected to avoid diagnostic errors[11].

Oral biopsy specimens can be affected by a number of artefacts resulting from crushing, fulguration or incorrect fixation and freezing[12]. There is a long standing controversy regarding selection both of the technique (incisional versus excisional) and of the surgical instruments used to avoid artefacts; punch biopsy may have some benefits [13].

Experimental studies have detected an increased frequency of neck metastasis from stage I and stage II OSCC after incisional biopsy and the presence of tumour cells have been noticed in the peripheral blood 15 min after incisional biopsies using a conventional scalpel[14, 15]. Consequently, it has been hypothesized that the use of a laser beam to obtain biopsy material could minimize seeding of cells but studies are needed to support this theory[16].

The limitations of comparing 2 biopsy results performed at different time has been highlighted in a study of 200 patients with leukoplakia, who underwent scalpel biopsies at different times with an agreement rate between two scalpel biopsies of only 56%. In addition, clinicians should be aware of possible under diagnosis after incisional biopsy-particularly in cases of "hybrid" forms of OSCC and non-homogeneous lesions, depending on the site where the biopsy is performed[17, 18].

A number of histological characteristics of the primary tumour, such as the grade of malignancy and depth of invasion, have been shown to have prognostic value in terms of tumour recurrence, lymph node involvement, and cause-specific survival hence, it is important for an incisional biopsy to be of sufficient size and depth to include part of the advancing margin of tumour[19]. Ideally, the deep margin should be included, but if this is not possible (e.g., in large tumours), the peripheral margin is often sufficiently representative to allow provisional assessment.

Finally, a high inter- and intraobserver variability in histologically diagnosing dysplasia has been described by many authors. The difficulty of accurately diagnosing dysplasia and reproducing those results can have significant implications for patients who are provided with false positive and false negative scalpel biopsy results. As already highlighted in this review, when two scalpel biopsies are performed at different times by different examiners, the agreement rate between them was only 56%[17]. It is evident that even incisional biopsies of suspicious lesions which have a limited reproducibility may, at times, result in a more or less aggressive surgical and/or radio-chemotherapeutic approach[11].

Vital staining

Toluidine blue (TB) staining is claimed to be a simple, inexpensive and sensitive adjunct tool for identifying early OSCC and high-grade dysplasias [20]. When a 1% aqueous TB solution is applied to a suspicious lesion for 30 seconds, this acidophilic metachromatic nuclear stain helps to differentiate areas of carcinoma in situ or invasive carcinoma from normal tissue. Although TB has been found to be highly sensitive and moderately specific for malignant lesions, it is far less sensitive for premalignant lesions with false negative rates of up to 58% reported for identifying mild-to-moderate dysplasia [10, 21].

Toluidine blue has also been demonstrated to help assess the status of margins around oral cancer at the time of resection [22]. Although toluidine blue test is helpful in identifying oral cancers, it should not be viewed as a substitute for biopsy, and a negative test does not preclude the presence of dysplasia or even oral cancer.