 |
| About Bioline | All Journals | Testimonials | Membership | News |
|
||||||
|
||||||
Journal of Cancer Research and Therapeutics, Vol. 7, No. 2, April-June, 2011, pp. 120-127 Review Article Human papilloma virus and oral infections: An update KL Kumaraswamy1, M Vidhya2 1 Department of Oral Pathology and Microbiology, Mahe Institute of Dental Sciences and Hospitals, Chalakkara, Mahe, India Code Number: cr11030 PMID: 21768696 Abstract Human papilloma virus (HPV) is one of the most common virus groups affecting the skin and mucosal areas of the body in the world today. It is also a known fact that HPV causes many lesions in the oral cavity. The most common conditions induced by oral HPV infection are usually benign-like oral papillomas, oral condylomas, and focal epithelial hyperplasia. Oral HPV infection has been found to be associated with some cases of oropharyngeal cancer, but it is not the main risk factor for this kind of cancer. HPV is been proved to be the causative agent in causation of cervical cancers without doubt, but its role as a etiologic agent in causing oral cancers needs to be evaluated and studied more to come into any conclusion. We have used review papers, case reports, cohort studies, case control studies, and various internet sources published from 1960 to 2011 to prepare this review of literature.Keywords: Human papilloma virus, hybrid capture, oncogenic, oropharyngeal cancer, polymerase chain reaction Introduction Human papilloma virus (HPV) has a wide disease spectrum affecting the cutaneous and mucosal areas of the body, ranging from benign common warts to invasive carcinoma. HPV infections have been reported in a number of body sites, including the anogenital tract, urethra, skin, larynx, tracheobronchial mucosa, nasal cavity, paranasal sinus, and oral cavity. [1],[2] Oral HPV infection may be associated with different diseases of oral cavities. HPV is one of the most prevalent infections in the world with several new cases diagnosed yearly. This article presents an update of the oral HPV infections. Virology, oncogenic potentiality, and diagnosis of oral HPV infection are also discussed. Virology HPV are small DNA viruses with about 7 900 nucleotide bases long. [1] There are more than 120 genetically different, yet closely related HPVs that are referred to as genotypes. [3] By definition, each type is defined by having less than 90% DNA base pair homology with any other identified HPV type. The genotypes are numbered in the order of their discovery. [3] It is not known why certain HPV types target skin on the hands or feet while others infect the oral mucosa and still others affect the genitalia of males and females. [4] Various types have specificity for certain human cell types and cause distinct types of lesions. [Table - 1] lists the HPVs that cause different lesions of the oral cavity. The HPV genome [Figure - 1] encodes DNA sequences for six early (E1, E2, E4, E5, E6, and E7) proteins associated with viral gene regulation and cell transformation, two late (L1 and L2) proteins which form the shell of the virus, and one region of regulatory DNA sequences. The different HPV types are characterized by genotypic variations in the DNA base-sequences of E6 and E7. It is these genotypic differences that permit stratification of the virus oncogenic phenotype into high, intermediate-, and low-risk types [Table - 2]. For example, the E7 protein of HPV 16 is more oncogenic than the E7 protein of HPV 6. [5] Oral Cavity and HPV Normal oral mucosa harbors HPV DNA ranging from 1 to 43%, which might depend on the techniques employed. [6] Oral HPV infection may be associated with different diseases of oral cavities. Oral HPV infection can be considered to be nuisance rather than a serious disease, except in some circumstances when the viruses are thought to be the cause for oral squamous-cell carcinoma. Oral HPV lesions can result in different clinical appearance, ranging from benign, hyperplastic, papillomatous, or verrucous lesions to carcinomatous changes. Transmission The mode of transmission of oral HPV is unclear. Since HPVs can establish latent subclinical infection, they may have been acquired early in life, that is, originated at birth from cervical infection in the mother (perinatal) but most transmission is horizontal. [7] HPVs can be sexually transmitted (orogenital contact) and also through nonsexual fomite transfer [8],[9] (example: moist towel sharing) since HPVs are highly resistant to lethal effects of heat and drying. Autoinoculation [2] of the virus from other cutaneous or anogenital sites is also possible. Oral Manifestations of HPV Infection Papilloma virus infections in oral mucosa were first demonstrated in animals more than 70 years ago. [10] Benign papillomatous lesions of oral cavity have been repeatedly produced in several animal species by experimental incubation with oral papilloma virus. [11] Many reports have investigated HPV in cytological and histologic samples derived from normal oral mucosa. HPV are known to be associated with a variety of oral lesion in man. HPV involvement in variety of benign oral lesions such as squamous papilloma, verruca vulgaris, condyloma acuminatum, focal epithelial hyperplasia, hairy leukoplakia, leukoplakia, papillary hyperplasia, fibroma, lichen planus, and verrucous carcinoma have been reported. [1] There are also many reports now that it is present in many oral carcinoma cases, implicating it as one of the etiologic factor for squamous-cell carcinoma. Focal Epithelial Hyperplasia Also known as Heck′s disease is a rare benign familial disorder characterized by multiple, soft circumscribed sessile nodular elevations of oral mucosa, associated with various HPV. [12] Koilocytosis, which is regarded as the cytopathic effect of HPV, is constantly present in these lesions. Papilloma virus particles and HPV antigens have been repeatedly observed in focal epithelial hyperplasia lesions, suggesting the viral etiology of the disease. HPV 1, 6, 13, and 32 have been demonstrated in Heck′s disease. [1],[13],[14] Oral Squamous Papilloma Oral squamous cell papilloma is a benign tumor, which can occur at any age but is most frequently seen in patients in third and fourth decades. Oral papilloma affects man as well as rabbits, dogs, and cattle. Papilloma virus etiology of oral papillary lesions in animals has been well established. Recent studies have also suggested HPV etiology of oral papillomas in man with the demonstration of HPV particles. HPV 6 and HPV 11 have been reported in many lesion studies. [1],[11],[15] Oral Condyloma Acuminatum It usually presents with multiple small, white or pink nodules, which proliferate and coalesce to form soft sessile growths. The surface contour in most cases is more cauliflower like than that of papillomas. They are very rare in oral cavity. Intranuclear viral inclusions, 45 to 52 nm in diameter, have been demonstrated by electron microscopy, stating the HPV etiology in some cases. HPV 6 and 11 have been isolated from these lesions. [1],[7],[16] Common Wart or Verruca Vulgaris Warts occasionally affect the oral mucosa. They appear as firm, whitish, sessile circumscribed exophytic lesions, which show conspicuous hyperkeratinization of the superficial epithelia and elongation of the rete ridges. Like the skin warts, oral verruca is clearly HPV-related. Both the mucosotropic HPV types HPV 6, 11, and 16 and cutaneous HPV types, e.g., HPV 1, 2, 4, and 7 have been reported. HPV 2 and HPV 4, frequently associated with cutaneous verruca vulgaris, have been detected in more than 55% of oral lesions. [1] Oral Lichen Planus Oral lichen planus (OLP) is relatively common disease of unknown etiology, which can involve skin and oral mucous membrane. OLP has been associated with a number of generalized medical disorders, notably diabetes and hypertension and a number of immunological disorders. The possible viral etiology is also proposed by the recent demonstrations of HPV in a high percentage of oral lesions. [1] Kashima et al. have demonstrated four of 22 OLP specimens being showing positive reaction for HPV structural proteins. [17] Maitland et al. reported that 87% (7/8) of OLP biopsies containing HPV DNA. [15] So far, HPV 11, 16, and HPV 16-related virus have been found in these lesions. Verrucous Carcinoma Verrucous carcinoma (OVC), a variant of squamous-cell carcinoma, has characteristic morphology and specific clinical behavior, frequently seen on buccal mucosa, gingival, and alveolus. Clinically, it appears as an exophytic growth producing cauliflower-like warty lesion, locally aggressive but well circumscribed. Histologically, surface epithelium shows acanthosis and keratinization with parakeratin plugging and clefting. Broad rete ridges with pushing margins but intact basement membrane is seen. The etiopathogenesis of OVC is unclear; however, studies have shown strong associations with tobacco use, including inhaled as well as smokeless tobacco, alcohol, and opportunist viral activity associated with HPV. More recently, studies have further confirmed the association between HPV and OVC by detecting HPV-DNA types 6, 11, 16, and 18 by polymerase chain reaction (PCR), restriction fragment analysis, and DNA slot-blot hybridization. [18] Oral Leukoplakia and Cancer Oral leukoplakia is a white patch or plaque-like lesion histologically showing a variety of epithelial changes ranging from harmless epithelial hyperplasia with hyperparakeratosis and hyperorthokeratosis to various degrees of epithelial dysplasia, including the in situ and early carcinoma. [19] Because a substantial percentage of oral carcinoma appears to develop in areas of leukoplakia, this entity has traditionally been considered as a precancerous lesion. [19] The etiology of oral leukoplakia is uncertain; the exogenous toxic agents such as tobacco and alcohol consumption have been implicated in the development of this lesion. [19] The possible viral etiology has been first suggested by light microscopic demonstration of HPV-suggestive changes. [1] According to many reports, HPV 16-related virus has been found in more than 80% of oral leukoplakias, irrespective of the degree of epithelial dysplasia. [15] Thirty percent of the leukoplakia lesions were positive for HPV 16 and 6/11 according to Sand et al. [20] In a review made by Miller and Dean, [21] HPV genotypes 2, 6, 11, and 16 were detected in 10.6% of cases of benign leukoplakia. Low-risk HPV types 6/11 were identified in 55.8% of HPV-positive leukoplakias compared with HPV 16/18 (28.8%) and HPV 2 (15.4%). Lind et al. [22] reported that 7 of 13 HPV-positive leukoplakias progressed to oral carcinoma within a 10-year period. Maitland et al. [15] have described about the HPVs being identified in oral leukoplakia and OLP, lesions that may show a low rate of progression to malignancy, and in cases of smokeless tobacco keratosis. The prognostic significance of HPVs in oral precancers is yet to be determined by large follow-up investigations but the 1996 study of 49 lesions (10 erythroplakias, 39 leukoplakias) followed by Nielsen et al. [23] for an average of 6.3 years found HPV in all three cases which eventuated in malignant transformation. Oral Hairy Leukoplakia Oral hairy leukoplakia (OHL) is a lesion frequently, although not exclusively, observed in patients infected by human immunodeficiency viruses. OHL is clinically characterized by bilateral, often elevated, white patches of the lateral borders and dorsum of the tongue. [24] Epstein-Barr virus appears to play a significant role in its etiopathogenesis, but the exact molecular mechanisms involved are not known. Many reports suggest the presence of Epstein-Barr virus. [25],[26] Human papillomavirus can sometimes be found in the oral mucosa among persons with OHL, but no evidence exists that this virus plays any role in causing OHL lesions. [27],[28] Oral Squamous-Cell Carcinoma Zur Hausen [29] has postulated the role of papilloma viruses in cancer of the cervix in 1976. Since then, HPV is established as the cause of almost 100% of cervical carcinomas. Although the risk factors in the pathogenesis of oral cancer includes infectious agents, diets low in fruit and vegetables, betel quid chewing, as well as smoking and alcohol consumption, [19] recently the possible etiologic role of oral precancer lesions and cancer has also been suggested by the discovery of HPV. [30] However, the association of HPV in oral precancerous and cancerous lesions has not been as consistent like cervical cancers. The prevalence of HPV infections in oral squamous-cell carcinoma has ranged between 10 and 100% [30],[31],[32],[33] [Table - 3]. Syrjanen et al. [36] gave the first report suggestive of viral etiology in oral squamous-cell carcinoma in 1983. Their study of 40 biopsy specimens from oral squamous-cell carcinoma revealed light microscope changes suggestive of HPV infection in 16 of the lesions. It would seem from this preliminary study that some 20% of oral carcinomas might be associated with HPV. HPV- DNA was first detected in oral squamous cell carcinoma in Germany in 1985. [37] According to recent reports, [38] HPV type 16 has been identified in 90% of HPV-associated head and neck tumors and has been found in 50% of oropharyngeal head and neck squamous-cell carcinoma. However, markedly varied estimates of HPV prevalence in premalignant head and neck lesions (0-100%) have made it difficult to clarify the timing and nature of the contribution of HPV to head and neck carcinogenesis. Smith et al.[33] (1998) have studied 93 cases of oral and pharyngeal cancer. They observed that both oncogenic and nononcogenic HPV types were found at a higher rate in people diagnosed with oral or pharyngeal cancers. More significantly, HPV was associated with an increased risk of cancer independent of exposure of alcohol or tobacco factors that are considered the major cause of oral cancer. Whim Syndrome Increased susceptibility to HPV infections is also been reported with a syndrome named WHIM, an acronym designation for a rare autosomal dominant syndrome characterized by warts, hypogammaglobulinemia, infections, and retention of mature neutrophils in the bone marrow (myelokathexis). Multiple, disfiguring, cutaneous warts, and susceptibility to HPV-related cervical dysplasia or carcinoma is been reported in women. Cipriani et al. have reported the occurrence of HPV-related oral squamous-cell carcinoma in two siblings with WHIM syndrome. The immune basis for WHIM syndrome is related to a mutation in chemokine receptor CXCR4, a 7-transmembrane protein expressed in a variety of stem, and progenitor cells, but its role in HPV infection is not well characterized. [39] The Oncogenic Mechanism The HPV′s mechanism of carcinogenesis is not completely understood. HPV can produce immortality in keratinocytes and acts alone even if different cofactors, still not completely located, are necessary for malignant conversion. The possibility of evolving into direction of malignancy depends on the type of virus, the synergic action with different physical, chemical, and biological agents, the genetic constitution, and the immune defense mechanisms of the host, all of which are able to modify the course of HPV infection. In the case of high-risk HPV infection and under favorable conditions, the viral genome is integrated into the host genome, which is the necessary event for the keratinocytes immortality. During this process of integration, the circular form of viral genome breaks at the level of the E1 and E2 regions, never at the level of the E6 or E7 region. Different studies have shown that the integrated part of the genome corresponds to E1, E6, and E7, while the regions from E2 to E5 are lost and are not transcribed in the tumors. The loss of E2 during this process of integration produces the loss of E6 and E7 control. Therefore, the sequences E6 and E7 are directly involved in the cellular cycle by inhibiting the normal functions of p53 and pRb, respectively. The protein p53 is known as the "genome′s guard" and in the case of DNA damage, the p53 can provoke the arrest of cellular division and assure the time necessary for DNA repair. If damage cannot be repaired, p53 is able to induce the programmed cellular death and prevent the propagation of DNA damage in subsequent generations of cells. In the case of other types of tumors, p53 is usually mutated and acts as a real oncogene. In the case of HPV infection, E6 suppresses the properties of p53 gene product, achieving the functional equivalent of the two hits required to knock out both alleles of a tumor suppressor gene. The mutations of p53 are normally not found. The E7 protein interacts with retinoblastoma protein (pRb), which is the crucial factor for the cellular cycle control. This interaction causes the release of the transcription factor E2F, which is now free to act and can stimulate the cellular division. E7 is also able to bind and inactivate the protein kinase inhibitors p21 and p27 and can interact with different proteins whose significance has still not been determined. [40] [Figure - 2] shows the diagrammatic representation of HPV-induced oral carcinogenesis. E6 and E7 can cooperate with cellular oncoproteins like ras and myc, which enables the virus to act at the level of growth factors and cellular and nuclear metabolism producing oncogenic cells. E6 and E7 can provoke directly DNA mutations of the host cell, probably by causing alterations of DNA repair mechanisms. This means that certain types of HPV are able to cause malignant lesions even without the action of other cofactors. [40] The p16 protein is a cyclin-dependent kinase inhibitor which regulates the activity of CDK4 and CDK6. It inhibits hyperphosphorylation of the retinoblastoma protein (pRb) and prevents its dissociation from E2F transcription factor and the subsequent progression of the S phase of the cell cycle. In HPV-infection, p16 is upregulated by the loss of the negative feedback control of pRb expression. [41] The resulting overexpression of p16 protein has also been extensively documented in HPV-positive carcinomas of the uterine cervix, vulvar, penis, and anorectal region, as well as those carcinomas related to HPV infection in oropharyngeal and sinonasal tract [42],[43] and it has been considered a useful surrogate marker of carcinomas related to HPV-infection. [39] The exact role of the immune response against high-risk HPVs is not completely clear. HPVs are obligatory intraepithelial pathogens that replicate at the superficial layers of the mucosa and epidermis where the cells are more differentiated. Both types of immune response (antibodies and cell-mediated) have been demonstrated in human beings. Cell-mediated immunity plays a crucial role in controlling HPV infection. [40] The antibodies against HPV can be of the type IgA, IgM, or IgG, reaching maximum levels 6 to 12 months after the beginning of the infection. There is an increased prevalence of antibodies against proteins E7 and E4 in patients with cervical intraepithelial neoplasia and with cervical carcinoma. It is possible that in the future, the measuring of the antibodies against E7 will become a marker to assess the response of a specific therapy. The presence of antibodies against E4 is associated with viral replication and is believed to coincide with the first host′s contact with HPV. The regression of HPV lesions is associated with a characteristic histologic response with participation of T lymphocytes and activated macrophages (cellularly mediated). In the case of immunosuppressed patients, the possibility of high-risk infections is increased because of the lack of immune response, the oncogenic effect of the drug administration, and chronic antigenic stimulation. [40] Diagnostic Methods to Detect HPV Infections Until recently, diagnostic laboratory testing for HPV was impossible since the virus does not grow in tissue cultures or in laboratory animals. Currently, with the recent technologic advancements in molecular biology techniques for HPV testing, scientists have isolated more than 120 different HPV types. Light microscopy Papillomaviruses cause epithelial proliferation characterized by epithelial thickening, prominent keratohyalin granules, acanthosis, and sometimes hyperkeratosis. [7] Koilocytes indicate the presence of productive HPV infection in exfoliated cells and biopsy specimens. They are squamous epithelial cells exhibiting perinuclear clearing and increased density of surrounding cytoplasm. Nuclear atypia (enlargement) hyperchromasia and double nucleation of superficial and intermediate cells are the hallmark of productive HPV infection. [44] But the sensitivity of infection detection is lower than the molecular methods discussed below. Electron microscopy Viral particles can be demonstrated in productive HPV infections, but HPV typing cannot be done. Under electron microscopy, HPV particles have been identified in a variety of oral squamous cell lesions, suggesting their HPV etiology. [1] The virions were identified in the nuclei of koilocytic and dyskeratotic cells. But as a diagnostic means of HPV infection, electron microscopy is laborious, time consuming, and limited to productive HPV infections only. [1] Nonproductive HPV infections which are usually caused by high-risk types cannot be detected. Molecular methods Molecular techniques can be broadly divided into those technologies that are not amplified and those that utilize amplification. In situ hybridization (ISH) / Dot Blot (DB) and Southern Transfer Hybridization (STH) require no amplification. Amplification techniques can be further divided into the following three separate categories: (1) target amplification, in which the assay duplicates fragments of DNA from a targeted gene sequence. PCR works by target amplification; (2) Signal amplification, in which the signal generated from each probe is increased by a compound-probe or branched-probe technology. Hybrid capture works by signal amplification; and (3) Probe amplification, in which the probe molecule itself is amplified (for example, ligase chain reaction). To date, target and signal amplification techniques, in addition to nonamplified techniques, have been applied to the detection of HPV. [45] Nonamplified techniques In situ hybridization ISH can be done directly on biopsies which allow localization of the target sequences and correlation with clinical appearance and histopathology. The presence of HPV-induced histologically equivocal lesions in biopsies can be confirmed by ISH. Viral transcription and integration can be studied with this technique in fixed tissue. Because ISH detects 25 HPV-DNA copies or more per cell, high-grade lesions that often contain lower amounts of viral HPV-DNA are nonsensitive with this technique. [5],[44] Southern blot and dot blot hybridization Southern blot hybridization is an important research tool and has been the technique generally used to classify newly identified viral types. [46] However, the method is restricted by a time-consuming and labor-intensive process, as well as a reliance on radiolabeled probes (isotopes). Commercial kits are not marketed for this method; rather, the process is entirely laboratory-based, using existing reagents and well-established methodologies. This intensive identification method therefore requires a sophisticated laboratory, with access to appropriate reagents and personnel skilled in advanced laboratory techniques. In Southern blot hybridization, the HPV genome is extracted from a specimen and the DNA chain is broken using enzymes. The product is integrated into a gel, which is subjected to an electric current-a process referred to as gel electrophoresis. The electrophoretic process separates the DNA based on the size of each fragment. The DNA fragments separated by this method are transferred to a nitrocellulose membrane and hybridized with cloned HPV genomic probes. These probes are then labeled, often using radioisotopes. The detection of the labeled DNA hybrids indicates that HPV is present in a given sample. Dot blot hybridization employs a simpler laboratory method than Southern blot but is rarely used due to its low sensitivity. [46] This method is similar to Southern blot hybridization, except that it does not include electrophoresis. Dot blot hybridization techniques formerly were used in two commercial HPV detection kits, Virapap® and Viratype®. These kits, previously available through the Digene corporation, are no longer marketed. [45],[47] Target amplification PCR is the most commonly used tool in the detection of HPV DNA. The natural history of HPV infection has been more clearly defined with PCR. [44] In theory, PCR can take a single double-stranded piece of DNA and amplify it to 1 billion copies after 30 cycles. [48] PCR frequently is used as a diagnostic tool in epidemiologic investigations of HPV, but the associated costs and technology requirements often are inappropriate for large screening programs. The inherent strength of the PCR-based methodology lies in its capacity to detect very small amounts of HPV DNA. At the same time, strict laboratory procedures and controls are critical in reducing contamination-related false-positive findings. [45] Signal-amplified techniques Hybrid Capture Technology Hybrid capture technology (HC), developed by the Digene Corporation, detects nucleic acid targets directly, using signal amplification to provide sensitivity comparable with target amplification methods (PCR). Digene has developed the following two products for the detection of HPV: the first-generation Hybrid Capture Tube (HCT) test and the second-generation Hybrid Capture II (HC II) assay. [45] Both assays detect "high-risk" HPV types. The HCT test detects the following high-risk types (as initially defined by Digene and supported by epidemiological studies): 16, 18, 31, 33, 35, 45, 51, 52, and 56. HCT was granted US FDA approval in May 1995. In March 1999, the US FDA approved Digene′s second-generation HPV detection kit (HC II). Four additional viral types were added to the high-risk category in the HC II test: 39, 58, 59, and 68. The level of detection of the second-generation HC II is rated at 5 000 viral copies per sample, or 1 pg of HPV DNA per sample (in contrast to HCT, which detects 10 pg). HC requires long single-stranded, or multiple oligonucleotide RNA probes to hybridize with the whole HPV genome in solution. RNA-DNA antibodies conjugated to alkaline phosphatase are then added to the hybrid, which bind in a nonsequence-dependent manner. The detection method uses a chemiluminescent reaction to provide a semiquantitative result. [5] More recent not much used Hybrid capture system (HC-3) will capture the target DNA sequence by using biotin-labeled oligonucleotide probes, which reduces the background noise that could be generated by endogenous DNA/RNA hybrids. Blocker probes are also included to enhance the specificity of the test. The specificity of HC-3 is improved compared with that of HC-2. [44] Gene Expression: DNA Microarray DNA microarray is a compilation of microscopic DNA spots on a solid surface by covalent attachment to a chemical matrix. Each gene on the solid supports referred to as spot or probe is usually less than 200 ΅m in diameter. Each spot has a unique sequence different from the others in the array and will hybridize only to its complimentary strand. This technique uses a DNA probe labeled with either a radioisotope or a fluorescent tag. The probe is applied to the fragment of DNA or RNA to be studied and by the rules of base pairing (A to T, C to G) "sticks" to its complementary sequence. This technology has made it possible to miniaturize methods of probe detection for DNA and allow detection of several thousand DNA or RNA sequences in one experiment. [49] DNA microarrays have been successfully used to identify global patterns of gene expression in different human neoplasms, including head and neck cancers. Many investigators have used microarrays to analyze gene expression changes in Head and neck squamous cell carcinoma (HNSCC) in tissues and cell lines, but little is known about the gene expression changes in HPV-associated HNSCC. The identification of molecular portrait of gene expression profiles in HPV-positive and -negative HNSCC, including their differences, could result in a better understanding of critical events during carcinogenesis. [49] Conclusion HPV has gained much interest recently, because it is accepted as important correlates of cervical cancer. Oral HPV infections have not been studied to the degree as those of the genital tract, although the evidence of association between certain tumors and HPV infection today is indisputable. Oncogenic HPVs are associated with oral malignancies, but its prevalence varies widely in different studies. Although study results are mixed, it seems possible that smoking and alcohol use may interact with HPV infection to increase a person′s risk of oral cancer. So, oral HPV infections need to be studied and investigated deeply so that it can guide us for future cancer prevention programs, including oral HPV vaccination for oral HPV infections. References
Copyright 2011 - Journal of Cancer Research and Therapeutics The following images related to this document are available:Photo images[cr11030f2.jpg] [cr11030t3.jpg] [cr11030t2.jpg] [cr11030f1.jpg] [cr11030t1.jpg] |
| |||||||||
