Molecular Insight Into Pathogenesis of Potentially Malignant Disorders of Oral Cavity
Early detection can decrease both morbidity and mortality associated with this neoplasm. However, screening for potentially
malignant disease is typically confounded by difficulty in discriminating between reactive/inflammatory lesions vs those lesions that
are premalignant in nature. Selected markers for cell proliferation, adhesion, apoptosis and lymphocytic infiltration were analysed
by immunohistochemistry in addition to static cytometry for DNA content. In the present review, we have discussed the molecular
pathogenesis of Oral lichen planus, oral sub mucous fibrosis and Leukoplakia.
Leukoplakia, Oral lichen planus, Oral sub mucous fibrosis, Precancer.
The sixth most common malignancy of the world is Squamous cell
carcinoma (SCC) of the oral and oropharyngeal region. Despite
numerous advances in treatment, long-term survival from this
disease remains poor. Early detection can decrease both morbidity
and mortality associated with this neoplasm. However, screening
for potentially malignant disease is typically confounded by
difficulty in discriminating between reactive/inflammatory lesions
vs those lesions that are premalignant in nature.1 Furthermore,
the histologic diagnosis of dysplasia can be subjective and is
thus prone to a considerable range of interpretation. Similarly, no
definitive, validated criteria exist for predicting which dysplastic
lesions are most likely to progress to cancer over time. Given this
state of science, the presence of dysplasia can only be used to
indicate that an oral lesion may have an increased risk of malignant
transformation. Molecular biomarkers capable of identifying
the subset of lesions likely to progress to cancer are required to
eliminate this clinical diagnostic dilemma.2
Oral Sub Mucous Fibrosis
Oral submucous fibrosis (OSMF) has also been previously
described as idiopathic scleroderma of mouth, idiopathic palatal
fibrosis, sclerosing stomatitis and juxta-epithelial fibrosis.3The
hallmark of the disease is submucosal fibrosis that affects most
parts of the oral cavity, progressive trismus due to rigid lips,
cheeks, pharynx and upper third of the esophagus leading to
dysphagia. The disease is mainly seen in Asian countries and the
prevalence is more in India. OSMF was first reported by Schwartz
in 1952 while examining five Indian women from Kenya, which he
called as “atrophicaidiopathica (tropica) mucosae oris“.4, 5 Later
in 1953, Joshi from Mumbai re-designated the condition as OSMF,
implying predominantly its histological nature. Its precancerous
potential was first reported by Paymaster in 1956. Rao in 1962
suggested that OSMF is a localized condition of collagen disease.6
The three main events that are modulated by TGF-b, which favors
the collagen production are: (1) activation of procollagen genes;
(2) elevation of procollagen proteinases levels: (a) procollagen
C-proteinase (PCP)/ bone morphogenetic protein1 (BMP1) and
(b) procollagen N-proteinase (PNP); (3) up-regulation of lysyl
oxidase (LOX) activity.6
Collagen is the most abundant protein in the human body and it plays
a critical role as a structural element of connective tissue. About 27
types of collagen have been recognized, which can be grouped into
seven broad classes. Major class is fibrillar collagen, among them
types I, III, and VI form a major part of connective tissue. Collagen
type VII forms the anchoring fibrils of oral mucosa.7, 8The
distinguishing feature is a unique type of triple helix, stabilized by
unusual cross-links. The processing of fibrillar collagen occurs in a stepwise manner. Procollagen genes are transcribed and translated
to form procollagen monomeric chains (procollagen precursor).9
Three of these monomers assemble into a trimer triple helix. This
is aided by disulphide bridge formation. Trimericprocollagen
chains are then acted upon by N- and C-terminal proteases (PCP
and PNP), to cleave the terminal domains.10After this cleavage
the collagen units form spontaneously into fibrils. The newly
formed fibrils are then covalently stabilized through cross-linking
to form a stable mature structure of collagen. The genes COL1A2,
COL3A1, COL6A1, COL6A3, and COL7A1 have been identified
as definite TGF-b targets.11These are early induced genes in
fibroblasts. They were identified by differential hybridization
of cDNA array. The transcriptional activation of types I and
VII collagen gene expression by TGF-b has been demonstrated.
This transcriptional activation of procollagengenes by TGF-b is
causing an increased expression of procollagen genes and hence
contributing to increased collagen level in OSMF.12, 13
The LOX is an essential enzyme for final processing of collagen
fibers into a stabilized covalently cross-linked mature fibrillar form
that is resistant to proteolysis. The LOX is dependent on copper for
its functional activity. Removal of copper leads to a catalytically
inactive apoenzyme. The LOX is synthesized as prolysyl oxidase
and conversion of this precursor into an active LOX is mediated
by BMP1 and takes place in the extra cellular space. During the
biosynthesis of LOX, copper is incorporated into LOX. Apart from
copper, LOX also contains another co-factor, a covalently bound
carbonyl prosthetic group – lysine tyrosylquinone (LTQ).14 The
LTQ is essential for the reaction mechanism of LOX, i.e. in the
formation of cross-links in the collagen fibers. Copper has been
suggested to play a structural role in stabilizing the LTQ. During
the process of cross-linking, copper plays an important role in
reoxidizing the reduced enzyme facilitating the completion of
the catalytic cycle.
Areca nuts have been shown to have a high
copper content, and chewing areca nuts for 5–30 min significantly
increases soluble copper levels in oral fluids.15This increased
level of soluble copper could act as an important factor in OSMF
by stimulating fibrogenesis through up-regulation of LOX activity.
Apart from this, the flavonoids that are present in areca nut have
been implicated in the process of enhancing the cross linking of
collagen fibers. In vitro studies have demonstrated the presence
of catechin to raise LOX activity.16They might be oxidatively
converted to quinones and hence, might resemble LTQ, which is
an important co-factor for LOX activity. This could be a possible
explanation for enhancing LOX activity. Apart from this process,
the in silico, molecular modeling experiments have revealed that
the direct interaction of flavonoids with collagen facilitates the
cross linking of collagen fibers.17, 18
The expression of LOX is regulated by various factors, among
which TGF-b is considered to be an important factor. TGF-b has
been found to strongly promote the expression of LOX both at
the mRNA and protein levels in various cell lines.19The exact
mechanism underlying this is not yet fully understood. This
could be indirectly via the elevation of BMP1 by TGF-b, as it
mediates the biosynthetic processing of LOX, i.e. conversion of
prolysyl oxidase to active LOX. The LOX activity is important for
formation of insoluble collagen due to cross-linking. The process
of cross-linking gives tensile strength and mechanical properties
to the fibers as well as makes the collagen fibers resistant to
proteolysis.20, 21 Increased levels and activity of LOX due to
increased BMP and copper levels, and further enhancement of its
activity by LTQ like flavonoids present in BQ, causes increased
crosslinking of the collagen fibers, tilting the balance towards a
fibrotic condition as present in OSMF.22
Oral Lichen Planus
Lichen planus is a chronic inflammatory disease that affects the skin
and the mucus membrane. Oral lichen planus (OLP), the mucosal
counterpart of cutaneous lichen planus, presents frequently in
the fourth decade of life and affects women more than men in a
ratio of 1.4:1. The disease affects 1–2% of the population. It is
seen clinically as reticular, papular, plaque-like, erosive, atrophic
or bullous types. Intraorally, the buccal mucosa, tongue and the
gingiva are commonly involved although other sites may be rarely
affected. Oral mucosal lesions present alone or with concomitant
skin lesions. The skin lesions present as violaceous flat-topped
papules in ankles, wrist, and genitalia, but characteristically the
facial skin is spared.23, 24
The etiology and pathogenesis of OLP has been the focus of
much research, and several antigen-specific and nonspecific
inflammatory mechanisms have been put forward to explain the
pathogenesis. Although mostly palliative, a spectrum of treatment
modalities is in practice, from topical application of steroids to
Abnormal nuclear DNA content (aneuploidy) is an indicator
of chromosomal aberrations and is associated with malignant
and premalignant lesions. In oral precancer studies, DNA index
measurement is thought to be more suitable for risk assessment of
an identified precancerous field and of less value in early diagnoses
despite the higher analytical sensitivity.26Aneuploid dysplastic
lesions are shown to develop SCC in a shorter period than diploid;
thus, measurement of DNA index might be valuable to determine
the time to cancer progression.27
Based on the studies, 2.5c exceeding rate (ER) and the proliferation
index of DNA content are shown to be useful parameters in
predicting malignant transformation. With more strict criteria
defined by Auer et al., aneuploidy is classified as 2.5cER more
than 35% and 5cER valued over 0%. These results are compatible
with the figures on potential risk of cancer development in OLP
(0.46.25%). In nuclear DNA content studies, many cellular
parameters can be detected with static cytometry analysis. Former
studies showed that in prostate and cervical carcinomas, the G2/M
phase is a strong prognostic marker in cancer development.28
A few additional reports exist on epithelial DNA content
measurements including OLP biopsies and cytology. The results are
conflicting and DNA content varies from diploid to aneuploid DNA content in OLP. The most important difference among these studies
seems to be the method used in DNA content measurement.29In
certain studies, cell separation technique was used for the image
cytometry measurement. In another study, exfoliative cytology
samples from OLP lesions were used. In static cytometry, both
the morphology and exact location of the measured cells can be
assessed simultaneously. Another distinct difference is that most
of the authors used the reticular form of OLP which is the most
unlikely form for malignant transformation. However, there is
one previous study where few erosive OLP lesions were classified
as aneuploid; hence aneuploid changes and DNA cytometry can
be suitable screening methods for OLP to detect the high-risk lesions.30
Cell cycle arrest helps in maintaining tissue integrity and
facilitating DNA repair mechanisms; however, at the same time,
entry into senescence could favor malignant transformation.
Inactivation of p53 is a frequent phenomenon in OSCC. This is
caused by mutations, presence of HPV virus and other molecular
alteration occurring in the p53 pathway.31
As p53 expression has been identified as a response to DNA damage,
the identification of p53 in OLP tissue is interpreted as an indication
of precancerous potential by some researchers.32In support to this
concept, Chaiyarit et al. showed an inducible nitric oxide synthasedependent
DNA damage and p53-elevated expression in OLP
patients. Another concept is that the high expression of p53 in OLP
is a result of the higher cellular proliferation. To prove that p53
expression in OLP is not just a result of the inflammatory process,
Safadi et al. compared the immunohistochemical expression of
p53 and its downstream effector p21WAF1 between OLP and
other inflammatory oral conditions and found significantly higher
expression in OLP.33
The word leukoplakia means white patch (leuko-white, plakiapatch).
It is considered as the premalignant lesions, but now
included in a broader term for common usage of tobacco in the form
of smoking and chewing. High-risk of malignant transformation
is encountered if the risk factors are not eliminated. It has been
reported that many oral squamous cell carcinoma develops from
the potentially malignant disorders. Correct diagnosis and the right
treatment at right time of potentially malignant disorders may
prevent malignant transformation of these lesions.34, 35
Loss of heterozygosity in a cell is the loss of normal function
of the allele of a gene whose homologous allele was previously
inactivated. This prior deactivation occurs in parental germ
cells and is transmitted to their offspring to generate cells that
are heterozygotic for the gene in question. The development of
this phenomenon in regions of the chromosome with tumor
suppressing genes could be related to the process of malignant
transformation. The loss of heterozygosity in oral leukoplakia
and its possible predictive value have been reviewed recently by
Zhang and Rosin, who establish that lesions with such loss limited
to chromosomes 3p and/or 9p would form part of the group of
leukoplakias of intermediate risk, with a 3.8- fold increase in risk
of malignant transformation, whereas lesions with loss from 3p
and/or 9p and loss from one or more of the 4q, 8p, 11q, 13q, and
17p chromosomes would be considered as high-risk leukoplakias,
with a 33- fold greater risk of progression to cancer.36, 37 Finally,
low-risk leukoplakias are considered those that do not present any
of the above losses of heterozygosity. Study of these molecular
alterations in resection margins complements histological
information and can demonstrate the presence of molecular
abnormalities at borders that are histologically free of disease—an
observation which could explain recurrences and the development
of oral squamous cell carcinoma. In fact, molecular confirmation
of complete resection of precancerous lesions was shown to be
strongly correlated with a decreased risk of oral carcinoma in
patients with high- or intermediate-risk leukoplakias, in contrast to
low-risk forms where no such correlation was found.38, 39
Microsatellites are repeats of non-coding DNA sequences that
occur normally within the human genome. Defects in the DNA
repair process can lead to microsatellites that are abnormally short
or long; this process has been termed microsatellite instability
(MI). MI is indirect evidence of an abnormal mismatch repair
(MMR) protein’s function (hMLH1, PMS2, MSH2, MSH6).
proposed mechanism relevant in Squamous cell carcinoma of
head and neck region (SCCHN)tumorigenesis is through promoter
hypermethylation. When MMR promoters are hypermethylated, it
provides indirect evidence of a higher chance that promoters of
tumor suppressor genes are hypermethylated too, and therefore
nonfunctional.40Alternatively, when a microsatellite repeat
replication error goes uncorrected, a germ line hereditary mutation
could result leading to inactivation of tumor suppressor genes and
uncontrolled cell and tumor growth. This concept of a mutator
phenotype provides an alternative to a multistage accumulation
of genetic alterations to explain head and neck tumorigenesis.
Specifically, the loss of function of a gene critical for the repair
of DNA damage greatly increases the mutation rate at other loci
leading to genome-wide instability.42, 43
In a study of 93 premalignant and 18 invasive SCCHN cases,
an increasing trend of MI was found from hyperplasias (6% of
specimens) to dysplasias/CIS (27%) and to invasive cancers (33%)
. A similar trend was found in another study where 15% of
dysplasias and 30% of invasive cases manifested MI at multiple
loci. Partridge et al. found as high as 55% of 31 leukoplakias and
erythroplakias to show MI. The incidences of MI found in these
and other studies in head and neck malignancies are significantly
higher than those reported in breast, skin and non-small-cell lung
cancers. The prevalence of MI appears to vary between tumor
Telomerase is an enzyme with polymerase activity formed from
a protein-RNA complex. It is produced in embryonic germline
cells and its function is to lengthen the telomeres by copying the
TTAGGG sequence. Telomerase plays an important role in the
formation, maintenance, and renovation of telomeres, preventing
cell apoptosis. It is suppressed by mature somatic cells after birth, allowing telomere shortening after each cell division.46
Overexpression of telomerase has been reported to be associated
with a range of neoplastic diseases.
The human telomerase
reverse transcriptase (hTERT) gene encodes the catalytic subunit
of telomerase and shows a positive correlation with telomerase
activity in different molecular studies. Overexpression in
leukoplakia, associated with increased telomerase activity, is an
early phenomenon in the process of oral carcinogenesis and one
that can be detected in precancerous stages. This phenomenon
shows a marked positive correlation with the degree of atypia,
showing severe dysplastic changes.47, 48
Califano et al. tested ten most common allelic events in a large
number of primary pre-invasive lesions and invasive HNSCC to
develop a molecular progression model. It involves inactivation
of many putative suppressor gene loci. Chromosomes 9p and 3p
appear to be lost early, closely followed by loss of 17p. Mutations
in p53 gene are seen in the progression of pre-invasive to invasive
lesions. Many other genetic events occur later during progression.
Other genetic events, such as amplification of cyclin D1 and
inactivation of p16 have been tested predominantly in invasive
lesions, but their precise order in the model was not determined.49
The pattern of specific gene mutation in OC patient may give
a clue to the aetiology of that particular tumor. Brennan et al.
analyzed the pattern of p53 mutation in HNSCC. They found that
the incidence of p53 mutation was much higher in patients who
were exposed to both tobacco and alcohol versus non-users.50
It has been suggested that alcohol appears to augment the effect
of smoking due to an increase in the absorbance of carcinogens
contained within the cigarette smoke.
evidences suggest that abstinence from cigarette smoking may
decrease the overall incidence of HNSCC.51
HPV positive oral and oro-pharyngeal cancer comprise a distinct
clinico-pathological entity. They are less likely to occur among
heavy smokers and drinkers, have lesser likelihood of p53 mutation
and have better cancer-specific survival. It has been suggested that
HPV positive tumours may have better prognosis by inactivating
Understanding the pathogenesis of the premalignant pathologies
is very important for planning the treatment protocol. Promising
technologies are being rapidly developed to assist in localization
of abnormal oral mucosa, in noninvasive and objective diagnosis
and characterization of identified mucosal lesions, and in therapy of patients with potentially malignant disorders.
- Lingen MW, Pinto A, Mendes RA, Franchini R, Czerninski
R, Tilakaratne WM. Genetics/epigenetics of oral premalignancy:
current status and future research. Oral Dis. 2011 Apr;17Suppl
- Rajendran R. Oral submucous fibrosis: Etiology, pathogenesis, and future research. Bull World Health Organ. 1994;72:985–96.
- Gupta MK, Mhaske S, Ragavendra S, Imtiyaz N. Review article:
Oral submucous fibrosis-Current concepts in etiopathogenesis.
People's J Sci Res. 2008;40:39–44.
- Rajendran R. Oral submucous fibrosis. J Oral MaxillofacPathol.
- Pundir S, Saxena S, Aggrawal P. Oral submucous fibrosis: A
disease with malignant potential-Report of two cases. J ClinExp
- Utsunomiya H, Tilakaratne WM, Oshiro K, Maruyama S, Suzuki
M, Ida-Yonemochi H, et al. Extracellular matrix remodeling in
oral submucous fibrosis: Its stage-specific modes revealed by
immunohistochemistry and in situ hybridization. J Oral Pathol Med. 2005;34:498–507.
- McPherson JP, Goldenberg GJ. Induction of apoptosis by
deregulated expression of DNA topoisomerase II alpha. Cancer Res. 1998;58:4519–24.
- Yoshida K, Yamaguchi T, Shinagawa H, Taira N, Nakayama KI,
Miki Y. Protein kinase C delta activates topoisomerase II alpha to
induce apoptotic cell death in response to DNA damage. Mol Cell
- Brown DC, Gatter KC. Monoclonal antibody Ki-67: Its use in
histopathology. Histopathology. 1990;17:489–503.
- Hirota M, Ito T, Okudela K, Kawabe R, Yazawa T, Hayashi
H, et al. Cell proliferation activity and the expression of cell
cycle regulatory proteins in oral lichen planus. J Oral Pathol Med.
- Taniguchi Y, Nagao T, Maeda H, Kameyama Y, Warnakulasuriya
KA. Epithelial cell proliferation in oral lichen planus. Cell Prolif.
- Ruutu M, Johansson B, Grenman R, Syrjänen S. Two different
global gene expression profiles in cancer cell lines established from
etiologically different oral carcinomas. Oncol Rep. 2005;14:1511–
- Klein HL. The consequences of Rad51 overexpression for
normal and tumor cells. DNA Repair (Amst) 2008;7:686–93.
- Castedo M, Perfettini JL, Roumier T, Kroemer G. Cyclindependent
kinase-1: Linking apoptosis to cell cycle and mitotic
catastrophe. Cell Death Differ. 2002;9:1287–93.
- Pirkic A, Biocina-Lukenda D, Cekic-Arambasin A, Bukovic
D, Habek M, Hojsak I. Tissue expression of proliferative antigens
(PCNA and Ki-67) in oral lichen ruber related to clinical status.
- Lindberg K, Rheinwald JG. Suprabasal 40 kd keratin (K19)
expression as an immunohistologic marker of premalignancy in
oral epithelium. Am J Pathol. 1989;134:89–98.
- Nie M, Zhong L, Zeng G, Li B. The changes of cytokeratin 19
during oral carcinogenesis. Zhonghua Kou Qiang Yi XueZaZhi. 2002;37:187–90.
- Downer CS, Speight PM. E-cadherin expression in normal,
hyperplastic and malignant oral epithelium. Eur J Cancer B Oral
- Bánkfalvi A, Krassort M, Buchwalow IB, Végh A, Felszeghy
E, Piffkó J. Gains and losses of adhesion molecules (CD44,
E-cadherin, and beta-catenin) during oral carcinogenesis and
tumour progression. J Pathol. 2002;198:343–51.
- Ebrahimi M, Boldrup L, Wahlin YB, Coates PJ, Nylander
K. Decreased expression of the p63 related proteins betacatenin,
E-cadherin and EGFR in oral lichen planus. Oral Oncol.
- Donetti E, Bedoni M, Boschini E, Dellavia C, Barajon I,
Gagliano N. Desmocollin 1 and desmoglein 1 expression in
human epidermis and keratinizing oral mucosa: A comparative
immunohistochemical and molecular study. Arch Dermatol Res.
- Dekker NP, Lozada-Nur F, Lagenaur LA, MacPhail LA, Bloom
CY, Regezi JA. Apoptosis-associated markers in oral lichen planus.
J Oral Pathol Med. 1997;26:170–5.
- Bloor BK, Malik FK, Odell EW, Morgan PR. Quantitative
assessment of apoptosis in oral lichen planus. Oral Surg Oral Med
Oral Pathol Oral RadiolEndod. 1999;88:187–95.
- Chang SK, Mirabal YN, Atkinson EN, et al. Combined
reflectance and fluorescence spectroscopy for in vivo detection of
cervical pre-cancer. J Biomed Opt. 2005;10:024–031.
- Rosenberg D, Cretin S. Use of meta-analysis to evaluate
tolonium chloride in oral cancer screening. Oral Surg Oral Med
Oral Pathol. 1987;67:621–627.
- Epstein JB, Scully C, Spinelli JJ. Toluidine blue and Lugol’s
iodine application in the assessment of oral malignant disease and
lesions at risk of malignancy. J Oral Pathol Med. 1992;21:160–
- Zhang L, Williams M, Poh CF, et al. Toluidine blue staining
identifies high-risk primary oral premalignant lesions with poor
outcome. Cancer Res. 2005;65:8017–8021.
- Leunig A, Betz CS, Mehlmann M, et al. Detection of squamous
cell carcinoma of the oral cavity by imaging 5-aminolevulinic
acid-induced protoporphyrin IX fluorescence. Laryngoscope.
- Zheng W, Olivo M, Soo KC. The use of digitized endoscopic
imaging of 5-ALA-induced PPIX fluorescence to detect and
diagnose oral premalignant and malignant lesions in vivo. Int J
- Huber MA, Bsoul SA, Terezhalmy GT. Acetic acid wash and
chemiluminescent illumination as an adjunct to conventional oral
soft tissue examination for the detection of dysplasia: pilot study.
Quintessence Int. 2004;35:378–384.
- Sokolov K, Aaron J, Hsu B, et al. Optical systems for in
vivo molecular imaging of cancer. Technol Cancer Res Treat.
- Soukos NS, Hamblin MR, Keel S, et al. Epidermal
growth factor receptor-targeted immunophotodiagnosis and
photoimmunotherapy of oral precancer in vivo. Cancer Res.
- Hsu ER, Anslyn EV, Dharmawardhane S, et al. A far-red
fluorescent contrast agent to image epidermal growth factor
receptor expression. PhotochemPhotobiol. 2004;79:272–279.
- Cawson RA, Binnie WH. Candida, leukoplakia and carcinoma:
a possible relationship. In: Mackenzie IC, Dabelsteen E, Squier
CA, editors. Oral premalignancy. 1. Iowa city: University of Iowa
Press; 1980. pp. 59–66.
- Wahi PN, Kehar U, Lahiri B. Factors influencing oral and
oropharyngeal cancer in India. Br J Cancer. 1965;19(4):642–660.
- Notani PN, Sanghvi LD. Role of diet in the cancer of the oral
cavity. Indian J Cancer. 1976;13(2):156–160.
- Williams HK. Molecular pathogenesis of oral squamous
carcinoma. MolPathol. 2000;53(4):165–172. doi: 10.1136/
- Jefferies S, Eeles R, Goldgar D, A’Hern R, Henk JM, Gore M,
et al. The role of genetic factors in predisposition to squamous cell
cancer of the head and neck. Br J Cancer. 1999;79(5–6):865–867.
- Tripathy CB, Roy N. Meta analysis of glutathione S-transeferase
M1 genotype and risk toward head and neck cancer. Head Neck.
- Brennan P, Lewis S, Hashibe M, Bell DA, Botteffa D,
Bouchardy C, et al. Pooled analysis of alcohol dehydrogenase
genotypes and head and neck cancer—review. Am J Epidemiol.
- Sidransky D. Molecular genetics of head and neck cancer.
- Wong DT, Biswas DK. Expression of c-erb B proto-oncogene
during dimethylbenzanthracene induced tumorigenesis in hamster
cheek pouch. Oncogene. 1987;2(1):67–72.
- Wong DT, Gallagher GT, Gertz R, Chang ALC, Shklar G.
Transforming growth factor-α in chemically transformed hamster
oral keratinocytes. Cancer Res. 1988;48(11):3130–3134.
- Brennan JA, Boele JO, Koch WM, Goodman SN, Hruban RH,
Eby YJ, et al. Association between cigarette smoking and mutation
of the p53 gene in head and neck squamous cell carcinoma. N Engl
J Med. 1995;332(11):712–717.
- Hollstien M, Sidransky D, Volgelstein B, Harris CC. p53
mutations in human cancer. Science. 1991;253(5015):49–53. doi:
- Nawroz H, Riet P, Hruban RH, Koch W, Ruppert JM, Sidransky
D. Allelo type of head and neck squamous cell carcinoma. Cancer
- Riet P, Nawroz H, Hruban RH, Coria R, Tokino K, Koch W, et
al. Frequent loss of chromosome 9p21–22 in head and neck cancer
progression. Cancer Res. 1994;54:1156–1158.
- Kamb A, Gruis NA, Weavar-Feldhaus J, Liu Q, Harshman K,
Tavtigian SV, et al. A cell cycle regulator potentially involved in
genesis of many tumor types. Science. 1994;264(5157):436–440.
- Papadimitrakopoulou V, Izzo J, Lippman SM, Lee JS, Fan
YH, Clayman G, et al. Frequent inactivation of p16ink4a in oral
premalignant lesions. Oncogene. 1997;14(15):1799–1803.
- Khuri FR, Lee FR, Lippman SM, et al. Randomized phase III
trial of low-dose isotretinoin for prevention of second primary
tumors in stage I and II head and neck cancer patients. Journal of
the National Cancer Institute. 2006;98:441–450.
- Shin DM, Khuri FR, Murphy B, et al. Combined interferonalfa,
13-cis-retinoic acid, and alpha-tocopherol in locally advanced
head and neck squamous cell carcinoma: novel bioadjuvant phase
II trial. J ClinOncol. 2001;19:3010–3017.
- Batsakis JG. Surgical excision margins: a pathologist’s
perspective. AdvAnatPathol. 1999;6:140–148.