HPV Detection Techniques

Cutaneous Group HPV

HPV types in the cutaneous group are not sexually transmitted. They infect cutaneous squamous epithelium, resulting in common warts (most commonly types 2, 4; also 26, 29, 57), plantar warts (most commonly type 1; also 2, 4, 60, 63), flat warts (most commonly types 3, 10, 28), and epidermodysplasia verruciformis (most commonly types 5, 8, although multiples have been reported).

HPV in Cervical Cancer

Carcinoma of the cervix has a major impact on the health of women globally as the second most common form of cancer and the fifth highest cause of death. The vast majority of cases occur in developing countries. In contrast, its incidence in women ranks 8th and 12th in the USA and UK, respectively. This decrease in incidence, as well as mortality, is attributable to the development of screening programs using a novel technology at the time, the Papanicolaou smear (Pap smear). This has resulted in a decrease of approximately 74% in incidence in the USA over the past 50 years.

Harald zur Hausen postulated that HPV was involved in the pathogenesis of cervical cancer and the virus was first identified in skin cancer. Professor zur Hausen and colleagues identified HPV16 and HPV18 in cervical cancer in the early 1980s. It is estimated that the majority of sexually active individuals become infected with HPV, but that the infection is typically transient and cleared by the immune system. Only persistent infection over the course of years and decades by HR HPV will result in the development of cancer.

HPV is the Cause of Cervical Cancer

It is now clear that HPV is the universal etiology of invasive cervical cancer throughout the world. The International Biological Study on Cervical Cancer (IBSCC) reported the detection of HPV in 93% of cervical carcinomas in a cohort of 932 patients from 22 countries using a polymerase chain reaction (PCR) assay for a 450 bp segment in the L1 open reading frame. This raised the possibility of an alternative etiology for cervical carcinoma in the 7% ( n = 66) of patients lacking detectable HPV templates. A follow-up study was performed to determine whether the absence of HPV DNA was genuine (i.e., these cases were true negatives) or false-negative results, which could be explained by the disruption of the PCR primer sequences (as could occur during viral integration), loss of the L1 open reading frame, or the absence of tumor in the tissue sampled. Since 450 bp exceeds the average length of DNA fragments in tissues fixed in formalin and embedded in paraffin (FFPE), the 66 negative samples from the initial study were analyzed for the presence of a 100 bp segment in the E7 open reading frame using specific primer pairs for 14 oncogenic HPV types, as well as determining the ability of the DNA templates to support the amplification of a control fragment of similar length (β-globin) and the presence of tumor in the tissue analyzed. When corrected for adequacy of PCR amplification and tumor content, the association of HPV with invasive cervical carcinoma was predicted to be 99.7%. Therefore, on a global basis, this represents the highest association of a cancer type with a specific cause. This universal association of HPV as the causal etiology of invasive cervical carcinoma provides a compelling rationale for the development of a vaccine to eradicate this common malignancy.

HPV16 and HPV18 are More Oncogenic

Not all HR HPV types are equal in their ability to induce malignancies. In a cohort of 1739 patients with invasive squamous cell carcinoma of the uterine cervix, 1487 (85%) were infected with one HPV type and 109 (6%) were infected with more than one. Among patients infected with one type, 54.6% had HPV16; 11% had HPV18; 4.4% had HPV45; and 3.4% had HPV31. Dual infection with HPV16 and HPV18 occurred in 36 (2.1%), HPV16 plus another type in 36 (2.1%), and HPV18 plus another type in 22 (1.3%). Many similar results have been published and HPV16 and HPV18 are responsible for 60–70% of cases of cervical carcinoma, and HPV31 and HPV45 are the cause of another 10%, depending on the study design and geographic locations.

HPV16, 18, and 45 are Found in Younger Women with Cervical Cancer

HPV16 and HPV18 are also found in younger mean or median age of women with cervical cancers in comparison to other HR HPV types. A recent worldwide HPV screening and genotype study with over 10 000 confirmed cervical cancer cases from 38 countries of different continents of the world showed HPV16 and HPV18 are the causes of 71% of cervical cancers. In the same study, HPV45 was shown to cause a slightly higher percentage of overall cervical cancer than HPV31 (6% vs 4%). When histologic types are grouped separately, HPV45 and HPV31 were presented, respectively, in 5% and 4% of squamous cell carcinomas but 12% and less than 1% of adenocarcinomas as well as of adenosquamous cell carcinomas. In this study, HPV45 had the lowest mean age (46.8 years) of women with cervical cancer, 3.2 years younger than HPV16 and 1.4 years younger than HPV18. Therefore, genotype HPV45 in addition to HPV16 and HPV18 in clinical screening may have added predictive value for patient outcome.

HPV in Head and Neck Cancer

The second most common malignancy caused by HPV is the cancers of the upper aerodigestive tract in the mucosa of the oral cavity, oropharynx, hypopharynx, larynx, sinonasal tract, and nasopharynx. A review of worldwide cases of squamous cell carcinoma of the head and neck reveals that HPV genomic DNA has been detected in approximately 26%. The incidence of oropharyngeal squamous carcinoma has increased in the USA, primarily in white men between the ages of 40 and 55 years. These patients do not have a high exposure to alcohol or tobacco, which are the recognized risk factors for squamous cell carcinoma of the head and neck, but are positive for high-risk types of HPV. These cancers, which typically occur in the tonsil and base of the tongue, are positive for HPV16 in 60–72% of cases. Risk factors included a high number of vaginal-sex partners and a high number of oral-sex partners.