Introduction
Lung cancer has become one of the most common cancers in the world. One to two million cases are being diagnosed each year. It has risen to one of the top ten leading causes of death globally. Tobacco smoking has contributed to about ninety percent of lung cancer in men and seventy-five percent in women. Apart from dietary causes and smoking, recent studies have shown that infectious diseases have a role in causing cancer. Research shows that contagious diseases are the third most common cause of cancers.
What Is HPV?
HPV (human papillomavirus) is a group of more than two hundred related viruses. They are a member of the Pappilomaviridae family of the epitheliotrophic DNA viruses. Epitheliotrophic DNA (deoxyribonucleic acid) viruses are double-stranded viruses that infect mucosal and epithelial cells. Epithelial cell differentiation controls the life cycle of the virus and its genetic expressions. HPV is usually spread through the vaginal, anal, or oral sex, though it can spread through other means. Many people may not display any symptoms. However, some may have warts in their genital areas, especially in the sexually transmitted variant. Some types of HPV can be a reason for cervical cancer, cancers of the head and neck, or anal or penile cancer.
What Are the Types of HPV?
Each human papillomavirus is designated its number or type. ‘Papilloma’ refers to a type of wart some papillomaviruses result in.
1. HPV lives in the epithelial cells found on the skin surface, the vagina, the anus, the vulva, the cervix, the head of the penis, the mouth, and the throat.
2. About sixty types of HPV can cause warts on the hands and feet.
3. Other types enter the body through sexual contact. They are attracted to the mucous membranes in the body, like the moist layers near the anus and the genitals.
4. HPV is generally categorized based on the risk potentials. They include:
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High-Risk Types: HPV 16 and 18 are examples of this type. About seventy percent of cervical cancers are caused by these viruses. HPV 31, 33, 45, 52, and 58 are other high-risk types.
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Low-Risk Types: Low-risk types of HPV include HPV 6 and 11. They cause about ninety percent of genital warts. They rarely cause cancers. These growths are like bumps and often resemble cauliflowers. They appear weeks or months after a sexual encounter with an infected partner.
How Does HPV Cause Lung Cancer?
There are three theories on how HPV infection in the thoracic visceral lung develops. They include:
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Transmission to the lung through the cervical tumor.
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High-risk sexual activity from an infected reproductive system to the mouth then travels to the throat and mouth.
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Through the air to the respiratory system and lungs.
Studies show that about eighty percent of HPV-infected women with lung cancer were found to have cervical intraepithelial neoplasia (development of abnormal cells in the cervix). A similar sequence of DNA (deoxiribonucleic acid) was observed in cervical smears, peripheral blood lymphocytes, and lung cancer. This suggests the probability that HPV is transmitted through the cervix to the lung tissues.
The lung, abundant in the endothelium, becomes infected by the virus, leading to lung cancer. Another source of spread is from mouth to mouth or mouth to genitalia. Another research showed that HPV in the oral foci can be transmitted to the lungs through the throat. Exhaled breath samples from lung cancer patients revealed the presence of HPV DNA. This proved that the virus could enter the lungs by respiratory gas flow. Hence, this points to a probability that HPV could be spread even through inhalation.
An active research area in recent years has been the molecular mechanism of HPV infections leading to lung cancer. The pathogenesis has been described in detail in a number of studies. The expression of numerous target genes can be controlled by HPV E6 and E7 oncogene proteins. Through several signaling pathways, proteins include p53, pRb, HIF-1, VEGF, IL-6, IL-10, Mcl-1, Bcl-2, cIAP-2, EGFR, FHIT, hTERT, HER-2, ALK, ROS1, and AhR increase lung cell proliferation, angiogenesis (formation of new blood cells), and cell immortalization (cells that stops proliferation). Therefore, these target genes and proteins may be therapeutic targets for HPV-associated lung cancers.
How Does HPV Enter the Lung Cell Receptors?
Entering a cell is crucial in any virus’s ability to infect a host cell. The particles of the HPV bind to the receptors on the cell's surface to begin the penetration into the host cell. Heparan sulfate proteoglycans (HSPG), widely distributed in the extracellular matrix and on the surfaces of most cells, including the basal membrane of type 1 alveolar epithelial cells and endothelial cells. It is thought to be the initial attachment receptor for HPV. Ultimately, the DNA material is transferred to the host cell. Though HPV may not show any symptoms in many cases, mutations and modifications of the components of the cells are seen.
How Are Lung Cancer Patients With HPV Treated?
Further investigations are required if lung cancer patients with HPV infections need to de-escalate treatment (evaluating whether the number of chemotherapies needs to be reduced). Some experts favor the idea of de-escalating the treatment. For instance, the fact that lung cancer patients with HPV have a better prognosis can be a fact to substantiate the requirement of de-escalating the treatment. Studies also show increased survival rates among lung cancer patients with HPV infection.
How Does HPV Affect the Survival of Lung Cancer Patients?
Numerous studies have been done on the effect of the HPV viruses on the survival rates of lung cancer patients. However, their results could be more consistent. Some experts found it to positively affect the survival rates, while others could not find any significant impact. More research needs to be done in this area to finalize the results.
Conclusion
The role of HPV in causing lung cancers is still plausible. However, it has been found to have an impact on the development of lung cancer, though not accurate on how influential it is. Some studies show that the presence of HPV can modify some treatments for lung cancer. However, more research is required to stabilize the conclusions.
