7. Viruses and Cancer

uncontrolled growth of abnormal cells in the body

• starts with stem cell, ends with terminally differentiated cell
• at each division one daughter cell remains the same and the other becomes more mature
• usually change morphology as they mature
• at end, cells do not divide but die after a certain amount of time (terminal differentiation)

• maturation sequence allows for proliferation
• terminal differentiation keeps the cell number constant
• cells transformed into cancer cells only at early steps of maturation in immature cells that are actively dividing - DNA synthesis is required to fix change in the genome and pass it on

any bulge or swelling, usually due to cellular growth

new abnormal cellular growth beyond the normal amount

having some abnormal growth but not spreading to distant sites via lymph or blood

having abnormal growth and potential for spreading distant sites via lymph or blood

to spread to distant sites via blood or lymph

• carcinoma - involves epithelial cells
• sarcoma - involves connective tissue
• leukemia and lymphoma - involve blood cells

• chemical carcinogens
• radiation
• viruses

• must be lysogenic or latent, not lytic, so it can persist in the infected cell and cause the required genetic changes
• must be able to alter the cell's growth pattern such that normal terminal differentiation is blocked and the cell keeps on dividing

• human papilloma virus
• dsDNA
• Types:
• cervical cancer - 16,18
• body warts - 1-4
• genital warts - 6,11

sexual contact

• infects epithelial cells on cervix
• HPV has 2 transforming genes E6 and E7 which inactivate a tumor suppressor protein

• most women are subclinical
• fewer women develop cervical dysplasia (precancerous)
• cervical carcinoma is least frequent

• appearance of the cervix
• papanicolaou smear

• cervical dysplasia (precancerous areas) - removed by cone biopsy
• cervical cancer - hysterectomy

• annual pap smear
• STI prevention
• two vaccines now on market

• epstein-barr virus
• dsDNA virus

close oral contact

• most people are asymptomatic but produce antibodies
• some people develop infectious mononucleosis
• most serious disease is cancer

• consists of large tumors made up of malignant lymphocytes, usually originating in the jaw or eye
• found primarily in African children

• arise in lymphoid tissue of the nasopharynx and metastasize early to lymph nodes in the neck
• occurs primarily in Asians

Bukitt's Lymphoma - malaria, mirrors distribution, depresses the CMI response

Nasopharyngeal carcinoma - genetic predisposition, environmental carcinogens

• biopsy
• for NPC, detection of elevated IgA to EBV

• chemotherapy
• radiotherapy
• surgery

• very difficult
• possibly remove cofactor

• Hepatitis B Virus
• partially dsDNA

areas with highest incidence are areas with highest prevalence of chronic carriers of HBV

• contaminated blood products
• sexual contact
• vertical transmission

• virus infects hepatocytes
• in some cells, establishes long-term infection
• transforming gene of virus encodes for a protein that inhibits DNA repair - accumulation of mutations in cell may lead to cancerous mutations

• most infections asymptomatic
• some infected people develop hepatitis
• fewer people develop HPC

• detection of alpha-fetoprotein
• imaging techniques

various types of surgery, liver transplantation

• vaccine against HBV
• break mother to child cycle
• identify chronic carriers and monitor for alpha-fetoprotein after 40
• chronic carriers should also avoid alcohol

• human T cell leukemia virus
• RNA retrovirus

blood-borne route and body fluids

• virus infects T lymphocytes - CD4 serves as receptor
• HTLV transforming protein acts by inhibiting DNA repair

same as any leukemia - anemia, fatigue, tendency to bleed

• detecting serum antibodies
• finding characteristic cancerous cells in a blood smear

chemotherapeutic drugs

• usual methods for blood-borne diseases and STIs
• screening blood units especially important
• testing pregnant women and warning them not to breastfeed or pasteurize their milk

• primary liver cancer - Hepatitis C virus
• Kapsoi's sarcoma - human herpes virus 8
• some forms of Hodgkin's diseases - EBV
• breast cancer - bovine leukemia virus?