Rare association of human papillomavirus DNA with esophageal cancer in Japan

Association between human papillomavirus (HPV) and oesophageal squamous cell carcinoma: a meta-analysis

SUMMARY

The oncogenic potential of human papillomaviruses (HPV) is well known in the context of cervical carcinoma; however, their role in the development of oesophageal squamous cell carcinoma (OSCC) is less clear. We aimed to determine the extent of the association between HPV infection and OSCC. A comprehensive literature search found 132 studies addressing HPV and OSCC in human cases, and a meta-analysis was performed using a random-effects model. There was evidence of an increased risk of OSCC in patients with HPV infection [odds ratio (OR) 2·69, 95% confidence interval (CI) 2·05-3·54]. The prevalence of HPV in OSCC was found to be 24·8%. There was an increased risk associated with HPV-16 infection (OR 2·35, 95% CI 1·73-3·19). Subgroup analyses showed geographical variance, with Asia (OR 2·94, 95% CI 2·16-4·00), and particularly China (OR 2·85, 95% CI 2·05-3·96) being high-risk areas. Our results confirm an increase in HPV infection in OSCC cases.

Human papillomavirus types 16 and 18 in esophagus squamous cell carcinoma: a meta-analysis

PURPOSE

A possible carcinogenic role of human papillomavirus (HPV) has been investigated in esophageal squamous cell carcinoma (ESCC) for nearly 30 years with mixed results. We performed a meta-analysis to assess the prevalence of "high-risk" HPV, HPV-16/18, in this disease. We also evaluated the association between infection with HPV-16/18 and ESCC risk by meta-analysis of case-control studies.

METHODS

Eligible studies published up to September 30, 2012 were retrieved via both computer searches of MEDLINE and EMBASE and manual review of references. A random-effects model was used to calculate summary prevalence and odds ratios (ORs) and corresponding 95% confidence intervals (CIs).

RESULTS

A total of 5755 cases of ESCC from 68 studies were included in this meta-analysis. Overall, 11.67% (95% CI, 7.74%-16.21%) of ESCC cases harbored HPV-16 and 1.82% (95% CI, 0.90%-2.95%) harbored HPV-18. In addition, meta-analysis of 10 case-control studies showed a significant increase in ESCC risk with HPV-16 infection (summary ORs = 3.55; 95% CIs, 2.05%-6.14%). However, this increased risk in ESCC was not made for HPV-18 infection (summary ORs = 1.25; 95% CIs, 0.46%-3.43%).

CONCLUSIONS

This meta-analysis indicated that HPV-16 and -18 can be detected in ESCC. HPV-16, but not HPV-18, is significantly associated with the risk of ESCC. However, it is early to conclude that both types of HPV are involved in esophageal carcinogenesis.

Role of human papillomaviruses in esophageal squamous cell carcinoma

Esophageal cancer (EC) is responsible for almost half a million deaths worldwide annually and has a multifactorial etiology, which may account for its geographical variation in incidence. In the last 30 years the potential of human papillomaviruses (HPV) as oncogenes or co-factors in the tumorigenic process of esophageal squamous cell carcinoma (ESCC) has been widely studied. While the etiology of HPV in cervical and certain other anogenital and aerodigestive cancers has been established, results regarding its role in EC have been largely inconclusive. A causal association can be evaluated only with a case-control study, where normal controls are compared to ESCC cases for the presence of HPV. We reviewed all studies investigating ESCC tissue for HPV DNA and identified 139 that met our inclusion criteria, of which only 22 were case-control studies. Our results support previous findings of higher levels of HPV detection in high-risk ESCC regions than in areas of low risk. In addition, we confirm that the role of HPV in ESCC remains unclear, despite an accumulation of studies on the subject. The variations in investigative technique, study design and sample types tested may account for the lack of consistency in results. There is a need for a meta-analysis of all case-control studies to date, and for large, well-designed case-control studies with adequate power to investigate the association. The potential benefits of prophylactic HPV vaccines could be evaluated if HPV is identified as an etiological factor in EC, highlighting the need for further research in this area.

Geographic origin is a significant determinant of human papillomavirus prevalence in oesophageal squamous cell carcinoma: systematic review and meta-analysis

BACKGROUND

Since the first reports in 1982 suggesting an aetiological role for human papillomavirus (HPV) in a subset of oesophageal squamous cell carcinomas (ESCC), the literature reporting HPV detection in ESCC has expanded rapidly. However no formal meta-analysis of this literature has been published yet. The objective of this study was to perform a systematic review and formal meta-analysis of the literature reporting HPV detection in ESCC.

METHODS

MEDLINE and Current Contents were searched through March 2012. The effect size was calculated as event rates and their 95% confidence interval (95% CI), with homogeneity testing using Cochran's Q and I² statistics. Meta-regression was used to test the impact of study-level covariates (HPV detection method, geographic origin of study) on effect size, and potential publication bias was estimated using funnel plot symmetry (Begg and Mazumdar rank correlation, Egger's regression, and Duval and Tweedie's trim and fill method).

RESULTS

Of the 1177 abstracts found, 152 studies were determined to be eligible for this meta-analysis. These 152 studies covered a total of 10,234 ESCC cases, analysed by different HPV detection methods in different geographic regions. Of these 10,234 cases, 3135 (30.6%) tested HPV-positive, translating to an effect size of 0.372 (95% CI 0.360-0.384; fixed effects model) and 0.290 (95% CI 0.251-0.31; random effects model). When stratified by HPV detection technique, there was a significant heterogeneity between the studies, but importantly, the between-strata summary comparison was not significant (random effects model; p = 0.440). In contrast, there was significant heterogeneity between the studies from the different geographic regions. In the maximum likelihood meta-regression, HPV detection method was not a significant study-level covariate, in contrast to the geographic origin of the study, which had a significant impact (p = 0.00005) on the summary effect size estimates. No evidence for significant publication bias was found in funnel plot symmetry testing. In the sensitivity analysis, all meta-analytic results appeared robust to all (n = 151) one-by-one study removals.

CONCLUSIONS

These meta-analysis results indicate that the reported wide variability in HPV detection rates in ESCC is not due to the HPV detection techniques, but is explained by the geographic origin of the study. These data substantiate the recently elaborated concept that ESCC might have a different aetiology in low-incidence and high-incidence geographic regions, HPV playing an important role only in the latter.

No association of high-risk human papillomavirus with esophageal squamous cell carcinomas among Koreans, as determined by polymerase chain reaction

The incidence of esophageal squamous cell carcinoma varies greatly with race and geographic location. It has been suggested that human papillomavirus (HPV) is involved in the pathogenesis of esophageal cancers, and that the incidence of esophageal cancers associated with HPV depends on the geographic location of the patient population. In studies performed on tumor specimens collected from areas with a low incidence of esophageal squamous cell carcinomas, HPV infection was detected in only a small percentage of tumors, whereas studies performed on specimens obtained from areas with a high incidence of esophageal squamous cell carcinomas provided strong evidence that HPV plays a significant role in esophageal carcinogenesis. To elucidate the putative role of HPV infection in the etiology of esophageal cancer in Korea, a total of 129 formalin-fixed, paraffin-embedded tumor specimens, eight fresh tumor tissues and 40 normal esophageal tissues were screened for HPV infection by polymerase chain reaction using consensus primers for HPV types 16, 18, 31, 33, 35, 52b and 58 and type 16-specific primers. SiHa cell line, formalin-fixed, paraffin-embedded cervical squamous cell carcinoma specimens were used as positive controls for HPV infection. Fragments of human beta-globin gene, which served as the internal controls, were successfully amplified from 102 of the 129 cancer specimens and from all the normal and fresh cancer tissues, while consensus and type 16-specific primers failed to detect HPV DNA sequences in any of the esophageal samples. The DNA extracted from the SiHa cell line and uterine cervical cancers were positive when both the consensus and type-specific primers were used. The results of this study suggest that HPV is not associated with esophageal carcinogenesis in Korea.

HPV infections and oesophageal cancer

The first reports suggesting an involvement of human papillomavirus (HPV) in the development of both benign and malignant squamous cell tumours of the oesophagus date back to 1982. Since then, a substantial amount of literature has accumulated on this subject, summarised in this review. To date, 239 oesophageal squamous cell papillomas have been analysed in 29 separate studies using different HPV detection methods, with HPV being detected in 51 (21.3%) cases. Many more squamous cell carcinomas have been analysed: of the 1485 squamous cell carcinomas analysed by in situ hybridisation, 22.9% were positive for HPV DNA, as were 15.2% of the 2020 cases tested by the polymerase chain reaction. In addition, evidence derived from large scale serological studies, animal experiments, and in vitro studies is discussed in the light of the highly variable geographical incidence rates of oesophageal carcinoma worldwide. It may be that the (multifactorial) aetiology of oesophageal cancer differs greatly between those geographical areas with a low risk and those with a high risk for this disease. Oncogenic HPV types seem to play an important causal role, particularly in high risk areas.

HPV infections and oesophageal cancer

The first reports suggesting an involvement of human papillomavirus (HPV) in the development of both benign and malignant squamous cell tumours of the oesophagus date back to 1982. Since then, a substantial amount of literature has accumulated on this subject, summarised in this review. To date, 239 oesophageal squamous cell papillomas have been analysed in 29 separate studies using different HPV detection methods, with HPV being detected in 51 (21.3%) cases. Many more squamous cell carcinomas have been analysed: of the 1485 squamous cell carcinomas analysed by in situ hybridisation, 22.9% were positive for HPV DNA, as were 15.2% of the 2020 cases tested by the polymerase chain reaction. In addition, evidence derived from large scale serological studies, animal experiments, and in vitro studies is discussed in the light of the highly variable geographical incidence rates of oesophageal carcinoma worldwide. It may be that the (multifactorial) aetiology of oesophageal cancer differs greatly between those geographical areas with a low risk and those with a high risk for this disease. Oncogenic HPV types seem to play an important causal role, particularly in high risk areas.

Expression of p21/WAF-1, status of apoptosis and p53 mutation in esophageal squamous cell carcinoma with HPV infection

Human papilloma virus (HPV) is regarded as a causative carcinogenic agent in anogenital squamous cell carcinoma (SCC), but there is controversy about its etiologic role in esophageal SCC (ESCC). In this study, we attempted to clarify whether HPV infection plays a crucial role in the development of ESCC by analysis of multiple factors. These included: detection of HPV DNA; evaluation of immunohistochemical assays for HPV-related cell cycle regulators and apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method; and genetic analysis of the p53 gene. Twenty of the 48 ESCC examined (42%) were found to be positive for the HPV genome by polymerase chain reaction. They comprised 16 cases with the HPV16 subtype, three with the HPV18 subtype, and one with both HPV16 and 18. Immunohistochemical analysis revealed that the expression of p21/WAF-1 was significantly decreased in HPV-positive cases (chi2 = 9.2614; P = 0.0023). Furthermore, the 10 apoptosis-negative (< or =10%) cases of HPV-positive SCC were almost exclusively p21/WAF-1-negative (chi2 = 12.1406; P = 0.0005), indicating the significance of the relationship between HPV infection and the phenotype that is expected from HPV-induced inhibition of p53. Although 14 cases possessed missense and deletion mutations of the p53 gene (of which four mutations were found in HPV-positive ESCC), no accumulation of the mutation was defined in the phenotype, suggesting that distinct mutation processes might be involved in HPV-negative and -positive ESCC. The data provide significant support for the hypothesis that HPV infection may play a crucial role in the oncogenesis of some ESCC.

Alcohol, smoking and papillomavirus infection as risk factors for esophageal squamous-cell papilloma and esophageal squamous-cell carcinoma in Italy

Esophageal papilloma, an infrequent benign tumor, and esophageal squamous-cell carcinoma sometimes appear to be associated with human papillomavirus (HPV) infection, HPV being implicated in anogenital carcinogenesis. Our aim was to assess whether there is any epidemiological difference in terms of risk factors for papilloma and cancer. From 1989 to 1996, a total of 12,011 patients (53% male, median age 52.7 years) were submitted to esophagogastroduodenoscopy by our Digestive Endoscopy Service. The genome of HPV was sought by PCR using 2 different primer sets. Of the total, 42 subjects (0.35%), 50% male with a mean age of 45.1 years, were suffering from esophageal squamous-cell papilloma and 45 (0.37%), 91% male with a mean age of 63.0 years, from esophageal squamous-cell carcinoma. Of these patients, only 2 with papilloma were HPV(+). Compared with the general endoscopic population, patients with papilloma do not present significantly different characteristics (even in terms of frequency of esophagitis and hiatal hernia). Those with carcinoma differ significantly both from the general endoscopic population and from those with papilloma in that they are more often male (p < 0. 0001), older (p < 0.0001) and drinkers (p < 0.0001); they differ significantly only from the general population, but not from the papilloma patients, in smoking habits. Papilloma appears to be neither a lesion involving a risk of development into a malignancy nor a marker for any such risk. Environmental factors, such as alcohol and smoking, appear to play a decisive role in esophageal carcinogenesis in northern Italy.

Human papillomavirus involvement in esophageal carcinogenesis in the high-incidence area of China. A study of 700 cases by screening and type-specific in situ hybridization

BACKGROUND

Human papillomavirus (HPV) DNA has been identified in esophageal precancerous lesions and carcinomas. However, there are marked variations in the prevalence of HPV infection reported in different studies. Most previous studies on HPV and esophageal carcinomas have been based on a limited number of biopsy samples studied by different HPV detection methods with highly variable sensitivity and specificity, making systematic studies of larger series clearly warranted.

METHODS

A series of 1876 surgical specimens (primary tumor, adjacent epithelium, regional lymph nodes, resection margins) from 700 patients surgically resected for an invasive squamous cell carcinoma of the esophagus in the high-incidence area of China was analyzed for the presence of HPV DNA with screening in situ hybridization (ISH) using biotinylated HPV DNA probes and followed by type-specific ISH for HPV 6, 11, 16, 18, 30, and 53.

RESULTS

Of the 700 esophageal carcinomas, 118 (16.9%) were shown to contain HPV DNA sequences by screening ISH. Positive signals were most frequent in the cancer cells (16.6%), more rare in the surrounding hyperplastic and dysplastic epithelia (5.6%), and infrequently present in the resection margins (0.2%). HPV signals were also detected in cancer cells in 6.9% of the lymph node metastases. HPV types 6, 11, 16, 18, and 30 account for 39.8% of the HPV-positive lesions, of which the high-risk types HPV 16 and 18 were present in 27.1% (32 of 118). Notably, 60.2% of the HPV-positive lesions contained DNA sequences other than HPV types 6, 11, 16, 18, 30, and 53.

CONCLUSIONS

This study reports the largest series of esophageal cancers ever analyzed for the presence of HPV DNA. Our results confirm the presence of common mucosal HPV types in esophageal carcinomas but also suggest the involvement of other (novel?) HPV types that are unusually detected in genital cancers in a significant proportion of these lesions. The results further indicate that HVP has an etiologic role in esophageal carcinogenesis, at least in the high-incidence area of northern China.

Detection of Epstein-Barr virus in esophageal squamous cell carcinoma in Taiwan

OBJECTIVE

Recently, an association between viral infection and the development of esophageal carcinoma has been reported, particularly the human papilloma virus (HPV) and Esptein-Bar virus (EBV). However, geographic variation in carcinogenesis is realized. In this study, we investigate the viral carcinogenesis and the biologic effect of viral infection on esophageal squamous cell carcinoma (ESCC) in Taiwan.

METHODS

To determine the association of viral infection (EBV and HPV) with ESCC, we applied polymerase chain reaction (PCR), immunohistochemistry, and in situ hybridization (ISH) to examine 119 surgical specimens from different sites of esophagus in 31 ESCC patients. Additionally, an immunoperoxidase method was used to detect EBV latent membrane protein-1 (LMP-1), p53, CD45RO (UCHL-1), Fas ligand (Fas L), and RNA ISH with oligonucleotide sequences was used to detected interleukin-6 (IL-6) mRNA.

RESULTS

By PCR, EBV DNA was detected in 11 cases (35.5%). Expression of EBERs in ESCC was further confirmed with ISH. Nonetheless, no LMP-1 expression was detected. On the other hand, human papillomavirus (HPV) was identified in only one case (3.2%) of ESCC. Furthermore, HPV was located by ISH in the distant normal region rather than in tumor cells. In EBV-positive cases, accumulation of p53 protein was detected in 10 lesions (91%); CD45RO+ lymphocytes together with expressions of FasL and IL-6 were respectively identified in 100%, 63.6%, and 54.5% of 11 EBV-positive lesions. Interestingly, in the EBV-negative cases (n = 20), p53 protein was detected in 40% of lesions; CD45RO 30%; FasL 50%, and IL-6 10%.

CONCLUSIONS

In this study, no correlation was found between the presence of EBV in ESCC and the patients' age, sex, as well as survival. Although our results indicate that EBV could be associated with ESCC, the clinical role of EBV in ESCC remains to be determined.

Papillomavirus in esophageal papillomas and carcinomas

Human papillomavirus (HPV) has been implicated as a possible etiological factor in the development of squamous-cell carcinoma of the esophagus. Published data demonstrating HPV DNA in these lesions have been conflicting, varying between failure to detect HPV DNA to detection of up to 60% to 70% of the biopsies harboring HPV DNA, mainly HPV 16 and HPV 18. We have analyzed esophageal carcinoma samples from 2 high-risk areas, China and South Africa, using a degenerate PCR approach. All amplified products were cloned and sequenced. A broad spectrum of HPV types was demonstrated in 10/29 samples from China and 9/34 samples from South Africa. HPV types detected included mucosal types HPV 6, 18, 51, 52 and 57; cutaneous types HPV 9, 20, 24 and 25; and the putative new HPV types DL231, DL428 and DL436, with HPV 6/51, 6/57, 20/9 and 20/DL231 occurring as double infections. HPV 6 predominated (4 samples) in 11 esophageal papillomas originating from patients in Europe and tested for HPV DNA. Other HPV types present included HPV 20, DL284 and DL436. Another putative new HPV type, DL416, was identified in a dysplastic lesion of the esophagus.

Human papillomavirus infection in esophageal carcinomas: a study of 121 lesions using multiple broad-spectrum polymerase chain reactions and literature review

To elucidate the putative role of human papillomavirus (HPV) infection in the etiology of esophageal cancer, 121 formalin-fixed, paraffin-embedded specimens originating from a non-high-incidence area for this carcinoma, from Slovenia, were screened for HPV infection using eight different polymerase chain reactions (PCR). Three different HPV consensus primer sets and four primer sets specific for HPV types 6, 16, and 18 failed to detect HPV DNA sequences in any of the tumor samples. Fragments of human beta-globin gene that served as internal controls were successfully amplified from 120 of 121 specimens. Our study confirms the opinion that most esophageal cancers originating from non-high-incidence geographic areas of this cancer are not associated with HPV infection. According to the studies reviewed, it is likely that HPV infection plays a much more significant role in esophageal carcinogenesis in those areas of the world with a high incidence of ESCC.

Human papillomavirus and oesophageal squamous cell carcinoma in the UK

Human papillomavirus (HPV) has previously been identified in up to 67% of squamous cell carcinomas of the oesophagus. In particular, HPV types of 16 and 18 are believed to play an important role in neoplastic transformation, by means of their oncoproteins E6 and E7. Most of these studies, however, pertain to areas of high incidence of squamous cell carcinoma of the oesophagus (the Far East and South Africa). It is not known if HPV plays any role in the development of oesophageal squamous cell carcinoma in the UK, where the tumour is relatively uncommon. The polymerase chain reaction was used to examine frozen tissue from 22 oesophageal squamous cell carcinomas for the presence of specific DNA sequences from oncogenic strains of HPV. PCR products were further analysed by Southern blot hybridization. No HPV sequences were detected in any tumours. These results suggest that these types of HPV are not associated with oesophageal squamous cell carcinoma in this country. It is unlikely, therefore, that HPV plays a significant role in the pathogenesis of squamous cell carcinoma of the oesophagus in the UK.

No evidence of known types of human papillomavirus in squamous cell cancer of the oesophagus in a low-risk area. Rotterdam Oesophageal Tumour Study Group

Controversial results regarding the presence and role of human papillomavirus in the development of oesophageal squamous cell carcinoma have been published. We used multiple broad-spectrum polymerase chain reactions to identify HPV DNA in oesophageal carcinomas from a low-incidence area. Paraffin embedded- and snap-frozen specimens from oesophageal cancer tissues of 63 patients were examined with a PCR technique with several primer pairs, capable of detecting most known HPV types. In none of the oesophagus cancer tissues could HPV DNA be detected. The role of HPV in this type of carcinoma in a low incidence area remains unclear.

Prevalence of HPV infection in esophageal squamous cell carcinoma in Chinese patients and its relationship to the p53 gene mutation

Human papillomavirus (HPV), in particular types 16 and 18, is positively associated with anogenital cancers and may be an important etiologic factor in their pathogenesis. The goal of our study was to investigate the role of HPV infection in the pathogenesis of esophageal squamous cell carcinoma (ESCC) and its relationship with the p53 mutation. We have examined ESCC collected from Sichuan, China, for the presence of HPV infection and p53 mutation. The presence of HPV DNA was detected by PCR-Southern analysis while the p53 mutation was analyzed by PCR-SSCP. High-risk HPV (types 16 and 18) DNA was detected in 32 out of 152 cases of ESCC examined. In contrast, HPV DNA was not detected in normal esophageal tissues excised from the distant end (tumor free) of resected ESCC. Mutation of the p53 gene was detected in 22 out of 55 cases of ESCC. The distribution of the 22 p53 mutation was: 5 in exon 5, 1 in exon 6, 5 in exon 7, 10 in exon 8 and 1 in exon 10. The p53 mutation was detected at a significantly lower rate in ESCC with HPV infection. Our results support a role of HPV infection in the pathogenesis of ESCC from a high-incidence area.

Presence of human papillomavirus in esophageal squamous cell carcinomas of Hong Kong Chinese and its relationship with p53 gene mutation

There is no scientific study that has investigated the association between human papilloma virus (HPV) and p53 mutation in Hong Kong Chinese patients with esophageal cancers. The aim of this survey is to evaluate in details the prevalence and relationship of HPV and p53 mutation in these patients with esophageal squamous cell carcinomas. Fresh tissues from the resected specimens of 70 Chinese patients (59 men, 11 women) with primary esophageal squamous cell carcinomas (20 well-differentiated, 36 moderately differentiated, and 14 poorly differentiated squamous cell carcinomas) were tested for the presence of HPV and p53 mutation using the polymerase chain reaction (PCR), single-strand conformational polymorphism (SSCP) analysis, and DNA sequencing. No HPV type 18 was detected, whereas HPV type 16 was identified in 8.6% (6 of 75) of the cases. p53 mutation was found in 44% (31 of 70) of the tumors. The mean ages of HPV-positive and HPV-negative groups of patients were 55 and 64 years, respectively (P = .046, t-test). There was no correlation between the prevalence of HPV and p53 mutation in these tumors. The presence of HPV and p53 also had no relation to the sex of the patients or to the grade of the carcinomas. It is concluded that the overall low prevalence of HPV in esophageal carcinomas may suggest that the virus may not play an important role in the pathogenesis of these tumors in Hong Kong Chinese patients. Also, p53 mutation and integrated HPV DNA are not mutually exclusive in esophageal cancer.

Human papillomavirus type 16 DNA in esophageal carcinomas from Alaska Natives

The possible etiological role of human papillomavirus (HPV) in esophageal carcinogenesis was evaluated in Alaska Natives in whom the incidence of esophageal cancer is 1.3 and 3.8 times higher than in US Caucasian men and women, respectively. Fixed paraffin-embedded esophageal tissues from 32 cases of squamous-cell carcinoma (SCC) and 3 cases of adenocarcinoma (AC) diagnosed between 1957 and 1988 were analyzed by polymerase chain reaction (PCR) and in situ hybridization for HPV DNA sequences. Detection of the human beta-globin gene by PCR was used as a control for sufficiency of DNA and its potential for amplification in the tissue samples. Twenty-five of the tumor tissues were considered adequate for PCR analyses; HPV DNA was detected in 10 of 22 SCCs and was not found in 3 ACs. Seven of the 10 HPV-positive tissues contained sequences from the E6 gene of HPV type 16. Koilocytosis, an epithelial change consistent with HPV infection, was found in 80% of the esophageal squamous-cell tumors with HPV DNA and in 75% of those without HPV DNA. The detection of amplifiable cellular DNA was related to recentness of diagnosis; however, the detection of HPV DNA within amplifiable specimens was not related to recentness of diagnosis. A 413-bp sequence from the L1 open reading frame of HPV 16 from esophageal tissue of 2 patients was identical to sequences previously identified in cervical cells from other Alaska Natives. Our results provide molecular evidence of HPV infection, especially type 16, in archival esophageal cancer tissues from 45% of those patients whose specimens contain adequate DNA for PCR analysis.