REVIEW ARTICLE
Spectroscopy in the Diagnosis of Oral Cancer Anjali Gupta*, Nandika Babele**, Tushar Phulambrikar***, Mayuri Jaitley** Abstract Oral cancer has a remarkable incidence over the world and a fairly strenuous prognosis, encouraging further research on the prognostic factors and new techniques for diagnosis that might modify disease outcome. It is known to develop from pre-existing potentially malignant oral lesions or de novo. Identification of progressing lesion at this stage aids in early diagnosis of the severity of the disease & institution of preventive & treatment measures. Screening of patients for signs of oral cancer and precancerous lesions has relied upon the conventional oral examination &confirming it by biopsy & subsequent histopathological examination. However, they have various limitations. As the emphasis shifts from damage moderation to disease prevention or reversal of early disease in the oral cavity, the need for sensitive and accurate detection and diagnostic tools is absolutely essential. These systems rely on the fact that the optical spectrum derived from any tissue will contain information about the histological and biochemical make up of that tissue. Such optical adjuncts may assist in identification of mucosal lesions including PML and OSCC, assist in biopsy site selection and enhance visibility of surface texture and margins of lesions and may also assist in identification of cellular and molecular abnormalities not visible to the naked eye on routine examination. The advantages of optical spectroscopy systems include diagnosis in real-time, non-invasive with high resolution surface and subsurface images. Key words: Spectroscopy, Oral cancer, Diagnosis (Gupta A, Babele N, Phulambrikar T, Jaitley M. Spectroscopy in the Diagnosis of Oral Cancer. journalofdentofacialsciences.com, 2015; 4(1): 7-11).
Introduction Oral cancer is the world’s sixth most common cancer, and global incidence and mortality rates *Senior Lecturer, **PG Student, ***Professor & Head, Department of Oral Medicine and Radiology, Sri Aurobindo College of Dentistry, Indore, Madhya Pradesh Address for Correspondence: Dr Nandika Babele, F-501, Shalimar Township, A.B. Road, Indore e-mail:
[email protected]
are increasing.1 However, oral cancer is predominantly a disease of developing nations, particularly prevalent in India and other south-east Asian countries due to the habit of tobacco usage. Although patients with early disease have better chances for cure and functional outcome, most patients present with advanced tumors when treatment is more difficult, more expensive and less successful compared to earlier intervention.2 The best way to improve outcomes is to improve early detection and diagnosis. Conventionally it has relied upon visual examination and biopsy but inter-individual expertise in physical examination
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as well as in histopathological confirmation, the demand for human and financial resources, the delay in time, amount of tissue gained via biopsy, and the obligatory invasiveness of a biopsy are factors affecting early diagnosis and thus adequate and early treatment of cancer.Recent research has demonstrated that optical methods can present a viable approach for improving screening and detection of oral malignancies. A number of biooptical methods are available which show the trendtowards an in situ identification of pathological changes in clinical practice. Methods A web-based search for all types of articles published was initiated using Medline/PubMed, with the key words such as oral cancer, prognostic factors of oral cancer, diagnostic method of oral cancer, and imaging techniques for diagnosis of oral cancer. The search was subsequently refined to spectroscopy technique for head & neck cancers. The sites of specialized scientific journals in the areas of oral and maxillofacial pathology, oral medicine, and oncology were also used. Discussion Light-based systems that are based upon the assumption that abnormal metabolic or structuralchanges have different absorbance and reflectance propertiesfor lights.3 Increased interest in optical systems using tissue spectroscopy in now been established to obtain diagnosis. Spectroscopy refers to the use of visible light dispersed according to its wavelength. It explores the optical phenomenon resulting from the interaction of light with biological tissues. Optical spectroscopy has the potential to detect malignant lesions earlier, before they become macroscopically visible, by probing tissue biochemistry & morphology in vivo in real time. Different spectroscopic techniques are utilized for the detection of premalignant oral lesions & oral malignancies. 1. Fluorescence Spectroscopy – It is a type of electromagnetic spectroscopy which analyses fluorescence from a sample. It involves using a beam of light, that excites the electrons in molecules of certain compounds & causes them to emit light of lower energy typically but not necessarily visible light. In case of www.journalofdentofacialsciences.com
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malignancythere are changes in the physical and chemical characteristicsof the tissues due to the subcellular architectural changesin cancer, such as nuclear grade and nuclear to cytoplasmratio, mitochondrial size and density, amount of keratin, and elastin to collagen ratio, and it is well known that all tissues fluoresce and malignant tissues fluoresce less than normal tissues, they have different spectral characteristics. Commonly detected fluorophores in living tissue include NADH, collagen, elastin & cofactors such as flavins (FAD, FMN). The fluorescence can either occur as autofluorescnece (if induced by UV light) or as a laser induced phenomena. Dysplastic & malignant tissues have different spectral characteristics as they tend to show increased red fluorescence & decreased green fluorescence. Significant increase in the red/green fluorescence ratio is an accurate predictor of dysplasia or malignancy. Optical fibres may be introduced intothe tissues through a hollow needle; the tissue signals areinterpreted by spectrometers.4,5 The reported sensitivity in fluorescence spectroscopy technologies was up to 81% and specificity was 100%.6 Autofluorescence studies using peak intensity at 337 nm showed sensitivity of 88% & specificity of 100%.7 Van Staveren found a sensitivity of 86% & specificity of 100% while distinguishing oral dysplasia from normal mucosa using autofluorescence.8 Light-induced fluorescence spectroscopy can distinguish between benign (normal and hyperkeratosis) and dysplasia with a sensitivity of 92% and a specificity of 95%.9 2. Enhanced Dye Fluorescence Photodynamic drug can be applied which enhanced porphyrins such as protoporphyrin IX (protoporphyrin IX is an important precursorto biologically essential prosthetic groups such as heme, cytochrome C, and chlorophylls). The fluorescence is slightly enhanced by using exogenously applied fluorescent drugs (e.g., 5-aminolevulinic acid induced protoporphyrin IX). Recent advances include the possibility to extract true spectra of Vol. 4 Issue 1
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single fluorophores (chemical compound that can reemitlight upon light excitation) by mathematically eliminating the undesired influences of scattering and absorption. As well, tumour-specific enzymes are about to be specifically targeted by fluorescent markers “smart probes” in order toimprove both sensitivity and specificity. Ebenezar stated that the diagnostic algorithm based on discriminant function scores obtained by fluorescence excitationspectroscopy (FES) method was able to distinguish well differentiated squamous cell carcinoma from normal lesions with a sensitivity of 100% and specificity of 100% .10 3. Elastic Scattering Spectroscopy- The system uses a wide band of wavelengths from 400 nm up to 700 nm and recovers the scatter power, scatter amplitude, and absorption species from the reflectance from a 100 micron spot, allowing imaging of tissue at high frame rate. Thus the ESS is the optical signature of the tumor which greatly depends on the morphology of the tumor & the acquired data reflects both the scattering and absorptive properties of that tissue. The structures that induce the scattering are the nucleus, chromatin concentration & subcellular organelles. The probe of the system should be in contact with the tissues, and no light is collected from the surface reflections. Lovat et al stated that the sensitivity was 92% and specificity was 60% and it differentiated high risk sites from inflammation with a sensitivity and specificity of 79% 11 .Elastic scattering spectroscopy recordings from normal and OSCC tissue may differ and studies on patients with leukoplakia have shown a sensitivity of 72.7% and specificity of 75% in differentiating cancer and dysplasia from benign lesions.12Assessment of nodal metastases had a sensitivity of 98% and specificity of 68%, but false positives were found in 40%.13 When used to measure the extent of invasion in the mandible, sensitivity was 85% and specificity 80%. 14 Muller et al used this to differentiate between various tissues & found the accuracy for normal to be 91.6%, abnormal 97%, dysplasia 64.3% & carcinoma 50 % when www.journalofdentofacialsciences.com
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compared with histopathology.15 There are 2 main limitations: a lack of data on oral lesions and a lackof correlation between the sites investigated using optical and surgical methods.16 It’s other clinical applications include biopsy examinations, measurement of surgical margins, measurement of oxygen saturation in tissues, measurement of uptake of photosensitiser for photodynamic therapy & measurement of concentration of drugs or chemotherapy in tissues. 4. Raman Spectroscopy– It is a laser-based technique that enables chemical characterization and structure of molecules in the sample. Within biological tissues 4 principle components contribute to the spectra; water, lipids (cell membrane), nucleic acids (DNA, RNA) and proteins (hormones). The resultant spectra from these structures give a characteristic picture of that tissue. Operator can alter the wavelength & hence can probe into differing depths within the tissue due to different wavelength penetration. It thus helps to obtain a vibrational spectroscopic picture of the tissue content, thus provide immediate real time histology. The reported sensitivity of this technique was of 80.5% and specificity of 86.2%.17 The major disadvantage is that it’s a complex procedure & expensive too. 5. Trimodal spectroscopy– It uses three independent optical diagnostic techniques (fluorescent spectroscopy, Raman spectroscopy and elastic scattering spectroscopy) to achieve better results, reaching sensitivity and specificity of 96% in differentiating between normal oral mucosa and dysplasia and OSCC and a sensitivity of 64% and specificity of 90% in distinguishing between dysplasia and OSCC.15 Tri-modal spectroscopy, although having the advantage of being accurate is however, expensive and time-consuming. 6. Ratio Imaging - This technique compares a photochemical or end metabolic product which is known to be increased in disease status to another product which isknown to be depleted. The 5-aminolevulinic acid enhances Vol. 4 Issue 1
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protoporphyrin IX which fluoresces red after excitation with blue light. The same excitation results in green fluorescenceof molecules such as NAD and FADH, which are depleted inhigh metabolic rate of malignant tissues. Shin statedthat the sensitivity of the fluorescence imaging techniques ranged from 60 to 97% and specificity from 75 to 99%.18 7. Differential Path-LengthSpectroscopy (DPS) – Differential path-length spectroscopy is a recently developed fibreoptic point measurement technique that measures scattered photons that have travelled, and their predetermined path lengths are measured. The spectrum is analyzed mathematically and is translated into a set of parameters that are related to the microvasculature and to the intracellular morphology. The reported sensitivity was 69%and specificity was 85%.19 8. Nuclear Magnetic Resonance Spectroscopy- This technology allows threedimensional study of atoms in the molecule; the larger the magnet, the more sensitive thedevice. It is possible to viewthe way of protein link up to DNA. 9. Infrared Spectroscopy- It distinguishes different biomolecules by probing chemical bond vibrations and using these molecular and submolecular patterns to define and differentiate pathological from normal tissues. 10. Magnetic Resonance (MR) SpectroscopyIt is a non-invasive diagnostic test for measuring biochemical changes in the tumors. While magnetic resonance imaging (MRI) identifies the anatomical location of a tumor, MR spectroscopy compares the chemical composition of normal tissue with abnormal tumor tissue. MR spectroscopy is conducted on the same machine as conventional MRI. The MRI scan uses a powerful magnet, radio waves, and a computer to create detailed images. Spectroscopy is a series of tests that are added to the MRI scan to measure the chemical metabolism of a suspected tumor. MR spectroscopy analyzes molecules such as hydrogen ionsor protons. Proton spectroscopy is more commonly used. There are several www.journalofdentofacialsciences.com
different metabolites, or products of metabolism, that can be measured to differentiate between tumor types. MRS provides biochemical information of compounds present in human tissue and cells. Human brain contains hundreds of metabolites, but the proton MRS can only detect a few of them as the least millimolar concentrations are necessary for the metabolites to be detected. Various metabolites detected are choline (Cho), creatinine (Cr), N-acetyl aspartate (NAA), lactate, myoinositol, glutamine and glutamate, lipids, and the amino acids leucine and alanine. The frequency of these metabolites ismeasured in units called parts per million (ppm) and plotted on a graph as peaks of varying heights. By measuring each metabolite’s ppm and comparing it to normal tissue, the type of tissue present can be determined. MRS demonstrates chemicals or metabolites within cancers that can be used as biomarkers to identify cancer and explore changes associated with hypoxia and cancer treatment. Of these, lactate is been found in metastatic nodes from HNSCC and has the potential to be used in the assessment of cancer hypoxia for assessing head & neck cancers.4 Conclusion Early detection of oral cancer is one of the most efficient ways to reduce the morbidity of the disease and its treatment. The information & the diagnostic potential provided by spectroscopic techniques allow us to understand the changes taking place during the onset of the disease & its subsequent progression. It not only helps in differentiating between normal & dysplastic mucosa but can also help in monitoring treatment & potential complications. They provide diagnosis in real time & are non-invasive. All imaging techniques presently require large multicenter controlled trials to determine the sensitivity & specificity of various spectroscopic techniques available to assess& improve their ability in detecting and management of potentially malignant & malignant oral lesions.
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