High‐risk HPV types and head and neck cancer

Although HPV16 has been strongly implicated in oropharyngeal carcinogenesis, the role of other high‐risk HPV types in the etiology of head and neck cancer remains unclear. To date, few data exist addressing the nature of the association between antibodies to oncogenic proteins of non‐HPV16 HPVs in relation to head and neck cancer. We examined the relationship between multiple HPV types (HPV6, 11, 16, 18, 31, 33, 45, 52, 58) and head and neck squamous cell carcinoma (HNSCC) in a large population‐based case–control study (1069 cases and 1107 controls). Serological measures for HPV types included antibodies to L1, E6 and/or E7. In a secondary analysis, we excluded HPV16 seropositive subjects to examine independent associations with other high‐risk HPVs. All analyses were adjusted for age, race, sex, education, smoking and alcohol consumption. Statistically significant associations were observed for HPV16, 18, 33 and 52 and risk of HNSCC after mutually adjusting for HPV types. Among HPV16 seronegative subjects, elevated risks of HNSCC were observed for HPV18 E6 (OR = 4.19, 95% CI = 1.26–14.0), HPV33 E6 (OR = 7.96, 95% CI = 1.56–40.5) and HPV52 E7 (OR = 3.40, 95% CI = 1.16–9.99). When examined by tumor type, associations with HPV18 and HPV33 remained statistically significant for oropharyngeal cancer, and HPV52 was associated with oral cancer. In addition, magnitude of associations for HNSCC increased markedly with increasing number of seropositive high‐risk HPV infections. High‐risk HPV types, other than HPV16, are likely to be involved in the etiology of HNSCC.     

Diagnostic Performance of HPV E6/E7 mRNA and HPV DNA Assays for the Detection and Screening of Oncogenic Human Papillomavirus Infection among Woman with Cervical Lesions in China

Background: Human papillomavirus (HPV) is the most common sexually transmitted infection worldwide and it is responsible for most cases of cervical uterine cancer. Although HPV infections of the cervix do not always progress to cancer, 90% of cervical cancer cases have been found to be associated with high risk HPV (HRHPV) infection. HPV DNA testing is widely used, along with Papanicolaou (Pap) testing, to screen for cervical abnormalities. However, there are no data on the prevalence of genotype-specific HPV infections assessed by measuring HPV E6/E7 mRNA in women representative of the Chinese population across a broad age range. Materials and Methods: In the present study, we compared the results with the CervicGen HPV RT-qDx assay, which detects 16 HR-HPV genotypes (Alpha-9: HPV 16, 31, 33, 35, 52, and 58; Alpha-7: HPV 18, 39, 45, 51, 59, and 68; and Alpha-5, 6: HPV 53, 56, 66, and 69), and the REBA HPV-ID assay, which detects 32 HPV genotypes based on the reverse blot hybridization assay (REBA) for the detection of oncogenic HPV infection according to cytological diagnosis. We also investigated the prevalence and genotype distribution of HPV infection with a total of 324 liquid-based cytology samples collected in western Shandong province, East China. Results: The overall HPV prevalences determined by HPV DNA and HPV E6/E7 mRNA assays in this study were 79.9% (259/324) and 55.6% (180/324), respectively. Although the positivity of HPV E6/E7 mRNA expression was significantly lower than HPV DNA positivity, the HPV E6/E7 mRNA assay showed greater specificity than the HPV DNA assay (88.6% vs. 48.1%) in normal cytology samples. The prevalence of Alpha-9 (HPV 16, 31, 33, 35, 52, and 58) HPV infection among these women accounted for up to 80.3% and 76.1% of the high-grade lesions detected in the HPV mRNA and DNA tests, respectively. The HR-HPV genotype distribution, based on HPV DNA and E6/E7 mRNA expression by age group in patients with cytologically confirmed lesions, was highest in women aged 40 to 49 years (35.9% for cytologically confirmed cases, Pearson correlation r value=0.993, p<0.001) for high-grade lesions. Among the oncogenic HR-HPV genotypes for all age groups, there was little difference in the distribution of HPV genotypes between the HPV DNA (HPV -16, 53, 18, 58, and 33) and HPV E6/E7 mRNA (HPV -16, 53, 33, 58, and 18) assays. HPV 16 was the most common HPV genotype among women with highgrade lesions. Conclusions: Our results suggest that the HPV E6/E7 mRNA assay can be a sensitive and specific tool for the screening and investigation of cervical cancer. Furthermore, it may provide useful information regarding the necessity for early cervical cancer screenings and the development of additional effective HPV vaccines, such as one for HPV 53 and 58. Additionally, gaining knowledge of HPV distribution may also inform us about ecological changes in HPV after the vaccination.     

Definition of an HPV18/45 cross-reactive human T-cell epitope after DNA immunisation of HLA-A2/KB transgenic mice

Although human papillomavirus (HPV) types 16 and 18 are the most common types associated with cervical cancer worldwide, other related HPV types such as HPV 35, 45 and 58 have significant prevalence in geographically distinct populations. For development of global prophylactic and therapeutic vaccine strategies, it is important to study immune responses against these viruses and to define the degree of cross-reactivity between related HPV types. To investigate the potential for T cell cross-reactivity after vaccination, HLA-A2/Kb transgenic mice were immunised with DNA plasmid constructs containing HPV18 and 45 E6 and E7. Splenocytes from immunised mice were tested in direct ELIspot assays against overlapping pools of HPV 18 peptides. Immunisation with either HPV18 or HPV45 E6 DNA produced dominant T cell responses against an epitope (KCIDFYSRI) that was shared between HPV18 and HPV45. This peptide was shown to bind to HLA-A*0201 but not Db or Kb molecules on the cell surface. Furthermore this peptide was shown to be immunogenic in vitro to human T cells from 2 out of 3 HLA-A2+ healthy donors. Collectively, these results demonstrate that HPV 18 and 45 E6 DNA vaccines are immunogenic in mice and demonstrate that cross-reactive T cell responses against closely related HPV types can be induced in vivo. The use of the HLA-A2/Kb transgenic mice allowed definition of an HLA-A*0201 binding peptide epitope that would have been rejected on the basis of predicted major histocompatibility complex binding affinity.     

Human papillomavirus (HPV) genotype distribution in invasive cervical cancers in France: EDITH study

Invasive cervical cancer (ICC) remains a significant cause of morbidity and mortality in France. Since human papillomavirus (HPV) is the necessary cause of ICC, the aim of this study was to assess the type-specific prevalence of HPV in ICC in France in order to locally evaluate the potential benefit of an HPV 16/18 L1 virus-like particles (VLP) vaccination. A total of 516 histological specimens collected in 15 centers were analyzed. Among them, 86% had a diagnosis of squamous cell carcinoma (SCC) whereas 14% were adenocarcinomas (ADC). HPV genotyping was performed using the INNO-LiPA assay allowing the specific detection of 24 HPV genotypes both high risk (HR) and low risk (LR). The overall HPV prevalence in ICC was 97%. The most prevalent genotypes were HPV 16 (73%) and HPV 18 (19%) followed by HPV 31 (7%), 33, 68, 45, 52 and 58 (4.1-2.3%). HPV 16 and/or 18 were associated with 82% of ICC, 10% being HPV 16 and 18 coinfections. While HPV 16 was the most prevalent type in both SCC (74%) and ADC (64%), HPV 18 was by far more prevalent in ADC (37%) compared to SCC (16%; p < 0.001). Multiple infections with at least two different HR HPV genotypes were observed in 22% of ICC. Given the high HPV 16/18 prevalence and taking into account possible production of crossneutralizing antibodies against other HPV types, HPV 16/18 L1 VLP vaccination would be expected to significantly reduce the burden of ICC in France.     

Human papillomavirus E7 protein detection as a method of triage to colposcopy of HPV positive women,in comparison to genotyping and cytology. Final results of the PIPAVIR study

The objective of the presented cross‐sectional‐evaluation‐screening study is the clinical evaluation of high‐risk(hr)HPVE7‐protein detection as a triage method to colposcopy for hrHPV‐positive women, using a newly developed sandwich‐ELISA‐assay. Between 2013‐2015, 2424 women, 30‐60 years old, were recruited at the Hippokratio Hospital, Thessaloniki/Greece and the Im Mare Klinikum, Kiel/Germany, and provided a cervical sample used for Liquid Based Cytology, HPV DNA genotyping, and E7 detection using five different E7‐assays: “recomWell HPV16/18/45KJhigh”, “recomWell HPV16/18/45KJlow”, “recomWell HPV39/51/56/59”, “recomWell HPV16/31/33/35/52/58” and “recomWell HPVHRscreen” (for 16,18,31,33,35,39,45,51,52,56,58,59 E7), corresponding to different combinations of hrHPVE7‐proteins. Among 1473 women with eligible samples, those positive for cytology (ASCUS+ 7.2%), and/or hrHPV DNA (19.1%) were referred for colposcopy. Cervical Intraepithelial Neoplasia grade 2 or worse (CIN2+) was detected in 27 women (1.8%). For HPV16/18‐positive women with no triage, sensitivity, positive predictive value (PPV) and the number of colposcopies needed to detect one case of CIN2+ were 100.0%, 11.11% and 9.0 respectively. The respective values for E7‐testing as a triage method to colposcopy ranged from 75.0‐100.0%, 16.86‐26.08% and 3.83‐5.93. Sensitivity and PPV for cytology as triage for hrHPV(non16/18)‐positive women were 45.45% and 27.77%; for E7 test the respective values ranged from 72.72‐100.0% and 16.32‐25.0%. Triage of HPV 16/18‐positive women to colposcopy with the E7 test presents better performance than no triage, decreasing the number of colposcopies needed to detect one CIN2+. In addition, triage of hrHPV(non16/18)‐positive women with E7 test presents better sensitivity and slightly worse PPV than cytology, a fact that advocates for a full molecular screening approach.     

新疆哈萨克族食管癌组织中HPV16 E6、E7基因的检测与p53的关系

目的探讨人乳头状瘤病毒(HPV)16型感染在新疆哈萨克族(哈族)食管癌发病中的作用,并分析HPV16感染与p53过表达之间的关系.方法采用聚合酶链(PCR)技术,检测41例食管鳞状细胞癌组织中HPV16 E6与E7基因表达差异;用LSAB免疫组织化学方法分析p53蛋白的表达.结果癌组织中HPV16 E6与E7基因阳性检出率分别为34.15%(14/41)和63.41%(26/41);用免疫组化检出p53蛋白阳性率分别在HPV16 E6阳性组(57.1%)与HPV16 E6阴性组(14.8%)间、HPV16 E7阳性组(42.3%)与HPV16 E7阴性组(6.7%)间均存在显著性差异(P＜0.05);用PCR检出HPV16 E6、E7基因在食管癌的高分化组、中低分化组中的检出率分别为7.69%(1/13)、46.43%(13/28)和38.46%(5/13)、75.00%(21/28),差别均有统计学意义(P＜0.05).结论提示p53基因突变与HPV16感染在哈族食管癌的发病过程中存在相互促进作用;另外,HPV16 E6与E7基因和哈萨克族食管癌病理组织学分级的生物学行为密切相关.     

食管癌高发区HPV检测及与p53的关系

目的 探讨食管癌高发区中人乳头瘤病毒（HPV）、爱泼斯坦-巴尔病毒（EBV）与食管癌发病的关系。并初步研究HPV感染与p53过表达之间的关系。方法 设计了多对引物进行PCR、原位杂交及原位PCR、免疫组化,并对30例高发区食管癌进行检测,结果 用PCR检出HPV-L1阳性率10.0%,HPV-16-E6阳性率60.0%,HPV-16-E7阳性率63.3%,HPV-18-E6及EBV的检出率分别为6.7%和0,p53蛋白的检出率为73.3%,用原位杂交和原位PCR检出HPV-16-E6阳性率均为53.3%.HPV-L1的低检出率及HPV-16E6、HPV-16-E7基因的较高检出率可能提示,在肿瘤细胞中HPV常以部分丢失的形式整合,而E6、E7常在整合中保留。结论 HPV-16型可能与高发区食管癌发生密切相关,而HPV-18、EBV则关系不大,p53突变在食管癌的发病中起重要作用。但其与HPV感染之间的关系不大。     

Performance of an HPV 16/18 E6 oncoprotein test for detection of cervical precancer and cancer

HPV testing is a better alternative for cervical cancer screening, but additional procedures are required for triage of HPV positive women. HPV encoded oncoproteins E6 and E7, as the main effectors of HPV carcinogenicity represent promising triage alternatives. To evaluate performance of the test, we included 155 women from a screening study and 59 from the same referral population attending colposcopy and with precancerous lesions. All were HPV-tested with HC2 and genotyped with LiPA, and cervical swabs were tested for HPV16/18 E6 oncoproteins. Histologic specimens were reviewed and adjudicated using p16 immunohistochemistry and 55 women had confirmed histologic HSIL, 31 (56.3%) associated with HPV 16/18, 23 with other HPV types and one HPV negative. Sensitivity and specificity were estimated with histologic HSIL/cancer as gold standard. E6 oncoprotein was detectable in all but one HSIL and in all cancers where HPV16/18 DNA was detected, but in none of the cases associated with other HPV types or HPV negatives. Among the few HPV16/18 DNA positive subjects initially without HSIL (n = 4) who were E6 oncoprotein positive, precancer was detected during follow-up in 2 out of 3 with available information. Estimated sensitivity for HPV16/18-related HSIL+ was 96.8% (95%CI = 83.8–99.8) and for all HSIL+ regardless of HPV type it was 56.4% (95%CI = 43.3–68.6). Specificity was 97.5% (95%CI = 93.7–99.0). E6 oncoprotein proved as a highly sensitive and specific marker for detection of HPV16/18-related HSIL lesions in this Honduran population with limited previous screening and may be useful as a triage method in screening programs, particularly in low income countries.     

Antibodies against high‐risk human papillomavirus proteins as markers for invasive cervical cancer

Different human papillomavirus (HPV) genes are expressed during the various phases of the HPV life cycle and may elicit immune responses in the process towards malignancy. To evaluate their association with cervical cancer, antibodies against proteins from HPV16 (L1, E1, E2, E4, E6 and E7) and HPV18/31/33/35/45/52/58 (L1, E6 and E7) were measured in serum of 307 invasive cervical cancer cases and 327 controls from Algeria and India. Antibody response was evaluated using a glutathione S‐transferase‐based multiplex serology assay and HPV DNA detected from exfoliated cervical cells using a GP5+/6+‐mediated PCR assay. Among HPV16 DNA‐positive cases, seroprevalence of HPV16 antibodies ranged from 16% for HPV16 E1 to 50% for HPV16 E6 and all were significantly higher than controls. Seroprevalence of E6, E7 and L1 antibodies for HPV18 and for at least one of HPV31/33/35/45/52/58 were also higher in cases positive for DNA of the corresponding type (50% and 30% for E6 of HPV18 and HPV31/33/35/45/52/58 combined, respectively). E6 and E7 antibodies were rarely found in controls, but cross‐reactivity was evident among cancer cases positive for DNA of closely phylogenetically‐related HPV types. E6 or E7 antibodies against any of the eight HPV types were detected in 66.1% of all cervical cancer cases, as compared to 10.1% of controls. E6, and to a lesser extent E7, antibodies appear to be specific markers of HPV‐related malignancy. However, even among cases positive for the same type of HPV DNA, approximately one‐third of cervical cancer cases show no detectable immune response to either E6 or E7.     

Looking beyond human papillomavirus (HPV) genotype 16 and 18: Defining HPV genotype distribution in cervical cancers in Australia prior to vaccination

Australia has implemented a high‐coverage HPV vaccination program but has not, to date, established the distribution of HPV types that occur in cervical cancers in Australia. This information is important for determining the potential for cervical cancer prevention with both current and broader spectrum HPV vaccines. We analysed 847 cervical cancers diagnosed 2005 to 2015 in tertiary centres in the three most populous Australian states with resolution of specimens containing multiple HPV types using laser‐capture microdissection. Archived FFPE tissue was reviewed by specialist pathologists, sandwich sectioned, and initially whole‐tissue sections genotyped for HPV. Samples were first genotyped using SPF10‐LiPA25 (version 1). Negative samples were screened with DNA ELISA kit HPV SPF10, followed by genotyping with SPF+ LiPA if ELISA positive. If still negative, samples were tested on a qPCR assay targeting the E6 region of HPV16, 18, 45 and 33. Of the 847 cancers (65.1% squamous, 28.7% adenocarcinoma, 4.3% adenosquamous, 2.0% other), 92.9% had HPV detected. Of the HPV‐positive cancers, 607 of 787 (77.1%) contained HPV16 or 18, 125 of 787 (15.9%) contained HPV31/33/45/52 or 58, and 55 (7.0%) another HPV type. There was a strong correlation between HPV type and age, with younger women most likely to have HPV16/18 detected and least likely HPV negative. Our findings indicate that cervical cancers diagnosed in Australia more frequently contain HPV16/18 than in international series. This could be due to cervical screening in Australia increasing the proportion of adenocarcinomas, in which types 18 and 16 more strongly predominate, due to prevention of squamous cancers.     

Naturally processed and HLA-B8-presented HPV16 E7 epitope recognized by T cells from patients with cervical cancer

Several major histocompatibility complex (MHC) alleles have been reported to present peptides derived from the HPV16 E7 oncoprotein to T cells. We describe an overrepresentation of the HLA-B8 allele (28.44%) in cervical cancer patients as compared to the MHC class I allele frequency in a local healthy control population (18.80%) and the identification of an HLA-B8-binding peptide TLHEYMLDL (HPV16 E7(7-15)), which is able to drive HPV16 E7-specific and MHC class I-restricted T-cell responses in peripheral blood lymphocytes from healthy individuals. TLHEYMLDL-specific T cells recognize the naturally processed and presented peptide on HPV16+ cervical cancer cells transfected with the HLA-B8 gene defined by IFN-gamma production. This peptide epitope is also recognized by freshly harvested tumor-infiltrating T cells or T cells from tumor-draining lymph nodes from patients with cervical cancer determined by flow cytometry as well as by tetramer in situ staining. HLA-B8-restricted HPV E7(7-15)-specific T cells reside predominantly in the CD8+ CD45RA+ CCR7+ precursor or in the differentiated CD8+ CD45RA+ CCR7- T-cell population.     

Animal models for development of therapeutic HPV16 vaccines (review).

In several types of human tumours a close association with oncogenic viruses has been established. Animal models mimicking these tumours with regard to their aetiology and expression of virus-related molecules have been developed. The rationale for development of the animal models was to create experimental systems allowing us to compare the efficacy of immunological and gene therapy protocols, with the final aim to optimize these therapeutic procedures prior to clinical trials. Anogenital carcinomas and particularly cervical carcinomas (CC) represent one of the aforementioned human oncogenic virus-associated tumour types. High-risk human papilloma viruses (HPV), particularly HPV16, 18, 31, 33, 45, and 56, are associated with nearly one hundred percent of CC. The only HPV proteins expressed in CC and representing the potential therapeutic targets are the non-structural viral gene products E6 and E7. The E6/E7 oncoproteins inactivate p53 and pRb tumour suppressor genes, they are required for maintenance of the malignant phenotype and their expression correlates with the transforming potential of HPV. Since the various HPV types do not cross-react with regard to the induction of both, humoral and cell-mediated immunity, the research of therapeutic vaccines is focused primarily on the HPV type 16, which is expressed in the majority, nearly 60%, of human squamous CC, and on the HPV16 E6/E7 oncogene products, which represent a target of choice for the therapeutic vaccination. The purpose of this review is to discuss the animal models of HPV-associated human tumours and the results obtained in these models with therapeutic vaccination against HPV-associated tumours. The prospects and limitations of the vaccination against HPV-associated tumours are also addressed.     

宫颈癌组织HPV58的检测及其E7基因的克隆和表达

目的　检测宫颈癌组织中人乳头瘤病毒 5 8型 (HPV5 8)并克隆表达其E7基因。方法采用GP5 /GP6 引物系统扩增 5 8例宫颈癌组织 ,将荧光偏振 (FP)检测技术与模板指导的末端延伸反应 (TDI FP)结合 ,检测HPV5 8,确定HPV5 8感染阳性宫颈癌组织。用特异引物从HPV5 8阳性标本中扩增HPV5 8早期表达蛋白E7基因 ,将其连入pGEM TEasy载体 ,获得克隆重组体HPV5 8E7 pGEM T ,并测序验证。将E7基因与pRSET A融合表达载体连接 ,获得E7表达重组体pRSET 5 8E7,转化大肠杆菌BL2 1(DE3) ,并用IPTG诱导表达。结果　 5 8例宫颈癌标本中 ,HPV5 8阳性 10例 ,占 5 2例HPV阳性标本的 19.2 %。从其中扩增到了HPV5 8E7基因并构建了其克隆和表达重组体。其表达重组体经IPTG诱导后 ,可表达Mr16× 10 3 的HPV5 8E7His6融合蛋白 ,表达量占菌体蛋白的 30 %。结论　欧美国家少见的高危HPV5 8在中国陕西人宫颈癌组织中并不少见。HPV5 8E7重组表达体可在大肠杆菌中高效表达 ,为HPV5 8相关肿瘤诊断试剂及疫苗的研制奠定了初步基础     

High-risk human papillomavirus E7 oncoprotein detection in cervical squamous cell carcinoma.

PURPOSE: Persistent infections by high-risk human papillomavirus (HPV) types are the main etiologic factor for cervical cancer. The objective of this study was to evaluate whether high-risk E7 oncoprotein is adequate as a marker for the detection of cervical cancer. EXPERIMENTAL DESIGN: HPV typing was done in biopsies from 58 cervical carcinoma and 22 normal cervical squamous epithelia. The HPV-16 E7, HPV-18 E7, and HPV-45 E7 oncoprotein levels were monitored by immunohistochemistry and compared with those of p16(INK4a) and Ki67. RESULTS: Fifty-five (94.8%) tumors were high-risk HPV-DNA-positive (46 HPV-16, 2 HPV-16 and HPV-18, 4 HPV-18, 1 HPV-33, and 2 HPV-45). HPV-DNA could not be detected in three tumors (5.2%). High HPV E7 oncoprotein levels were shown in 57 cervical cancers (98.3%), without correlation between expression levels and tumor stages. CONCLUSION: This is the first study which systematically analyzes the levels of the major HPV oncoproteins in cervical carcinomas demonstrating that the high-risk HPV E7 proteins are regularly expressed in these cancers. This suggests that high-risk E7 oncoproteins are necessary for cervical cancers and apparently essential as tumor marker.     

Vaccine-related HPV genotypes in women with and without cervical cancer in Mozambique: burden and potential for prevention

Knowledge about the burden of Human Papillomavirus (HPV) infections in Sub-Saharan Africa is very limited. We collected cervical samples from 262 women from the general population and 241 tumor samples from women with invasive cervical cancer in Mozambique and tested them for HPV genotyping by the SPF(10)-LiPA(25) PCR system. Among the 195 women without cervical abnormalities by cytology HPV prevalence was 75.9%. In this group of women, the most frequently identified HPV types among HPV-positive women were in descending order of frequency: HPV51 (23.6%), HPV35 (19.6%), HPV18 (14.2%), HPV31 (13.5%) and HPV52 (12.8%). In women with cervical cancer HPV DNA detection was 100%. The type-specific distribution of the most frequent types in descending order of frequency was: HPV16 (47.0%), HPV18 (31.3%), HPV51 (14.8%), HPV52 (14.3%), HPV45 (12.6%), HPV35 (10.4%), HPV33 (4.8%) and HPV31 (2.6%). HPVs 16/18 and HPVs 16/18/31/45 were detected in 71.7% and 80.9% of cervical cancer tissue, respectively. While HPVs 51 and 35 were the two most common types in cytologically normal women in Mozambique, HPVs 16 and 18 remained the two most frequently identified types in cervical cancer. The introduction of an efficacious HPV 16/18 vaccine could potentially prevent the occurrence of 72% of cervical cancer cases and up to 81% of the cases if full cross-protection against HPVs 31 and 45 is assumed.     

Prospective study on cervical neoplasia IV. Presence of HPV antibodies

Sera collected in the course of a prospective study carried out in Prague in 1975–1983 were assayed for the presence of human papillomavirus (HPV) antibodies. Women with cervical neoplasia proven by biopsy at enrollment possessed antibodies to peptides derived from E2, E4 and E7 proteins of HPV16 and to virus‐like particles (VLPs) of HPV16, ‐18 and ‐33 significantly more frequently than matched controls. Women without cervical neoplasia at enrollment who developed the disease in the course of the study differed from matched controls by a higher prevalence of antibodies against VLPs of HPV16 and ‐18 but not against early antigens of HPV16. In 19 of the latter subjects, paired serum specimens were tested, the first samples having been taken at enrollment and the second at diagnosis. Development of the disease was associated with seroconversion from negativity to positivity to at least one HPV antigen in 11 (57.9%) women. Int. J. Cancer 80:365–368, 1999. © 1999 Wiley‐Liss, Inc.