子宮頸癌形成的原因現今已知與乳狀突病毒(HPV)有密切關係。當子宮頸上皮細胞受到感染，並由此乳狀突病毒提供子宮頸額外的核酸(DNA)，子宮頸細胞便容易發生突變而產生癌症。人類乳突狀病毒總計至今已有九十種以上，人類乳突狀病毒可分為“低危險亞型”與“高危險亞型”兩大類。現今已經知道至少有35種高危險亞型的人類乳突狀病毒是與子宮頸癌的發生形成有關，其中最重要與常見的型態種類有HPV-16,18,31,33,35,52,58等數種，而這些高危險亞型的人類乳突狀病毒感染與子宮頸癌前期病變或子宮頸癌的相關性，約在百分之80至90之間，至今許多醫學論文也都已證實人類乳突狀病毒是導致產生子宮頸癌最主要的原因之一，總結這些相關論文，可得下列數項結論：

1.乳狀突病毒的染色體基因可分為”L”與”E”兩大類，當子宮頸細胞感染乳狀突病毒後，乳狀突病毒的染色體基因便進入人體的子宮頸細胞中，當乳狀突病毒的染色體E2斷裂後，它的病毒基因便會和子宮頸細胞的染色體基因結合，這樣病毒的E6基因便會和子宮頸細胞的癌症抑制基因(tumorsuppressorgeneP53)結合,而阻礙了P53基因抑制細胞過度生長的作用，同時E7會和子宮頸細胞的E2F酵素結合,而導致另一個癌症抑制基因(Rb-E2F)的控制細胞增值功能喪失，就因為E6及E7的作用，便會導致子宮頸細胞的增值失控與癌病變形成。在子宮頸癌形成原因中，僅有少數是與乳狀突病毒沒有關聯的，其原因可能的是直接在子宮頸細胞的癌症抑制基因(P53,Rb)上的基因突變，而導致癌症抑制基因的功能喪失，進而產生癌病變。

2.乳狀突病毒的感染途徑主要為經由性行為接觸，或經由血液及體液感染，不過亦可以經由懷孕與生產途徑來傳染，現今已知有多位性伴侶，年齡過早有性行為，或與色情職業的高危險對象發生性行為等的不安全性行為，均會增加乳狀突病毒的感染機會。我們先前的研究已顯示在台灣，乳狀突病毒在有性行為女性的感染率約為百分之十五至二十五左右，不過在未婚沒有性行為的年輕女性亦有約百分之四至七的感染率，亦有文獻報告指出在美國大學年輕未婚女學生的感染率約有三分之一，其中四分之一將會形成病毒的持續性感染(persistentinfection)，而高危險亞型HPV持續性感染的婦女中、約三分之一將來會形成子宮頸癌前期病變(CIN)，如罹患CIN未被治療或未被發現，則4%(CINI)至30%(CINIII)的患者將來會演變成子宮頸癌，所以高危險亞型的HPV持續感染婦女，是很需要被照顧的子宮頸癌高危險群。所以對乳狀突病毒的感染認知與衛教將會是一個是很重要的課題。

（1）感染人類乳突狀病毒的婦女，四分之一將會形成乳突狀病毒的持續性感染者。

（2）許多醫學文獻已證實感染高危險亞型人類乳突狀病毒的婦女約三分之一會形成子宮頸癌前期病變。

（3）子宮頸癌前期病變患者如未治療或未被發現，則4%(CINI)至30%(CINIII)的患者將來會演變成子宮頸癌。

基於上述原因，所以大家已有共識：如果婦女感染高危險亞型的人類乳突狀病毒﹙HPVDNAtype16、18、31、33、35、39、45、51、52、56、58、59、及68﹚，那麼她就是屬於子宮頸癌的高危險族群了。因為已婚的婦女約百分之二十是有人類乳突狀病毒的感染，而這些也正是好發子宮頸癌的高危險群婦女，然而現在台灣只有百分之二十至三十的已婚婦女是有做過子宮頸抹片檢查的，所以遺漏了很多的潛伏患者(平均計算，遺漏了百分之七十的高危險群)，所以以類似“肝癌的肝炎病毒檢驗模式”，利用乳突狀病毒基因檢測來做子宮頸癌高危險群的篩檢，經由乳突狀病毒的基因檢驗技術，事先得知哪些婦女是屬於較容易發生子宮頸癌的高危險群婦女，那麼將可以提高這些婦女對疾病的認知，讓他們對疾病不再有漠視的情形存在，進而提高這些婦女定期做子宮頸抹片的意願。雖然人類乳突狀病毒的感染，至今仍無有效藥物可供治療，但是對於這些較易發生子宮頸癌的婦女，以密切追蹤及觀察來面對、並衛教定期做子宮頸抹片，將可以避免遺漏了這些屬於較容易發生子宮頸癌的高危險群婦女不去做抹片。

現今許多國家已經開始採用人類乳突狀病毒的基因檢驗來做全國婦女的子宮頸癌高危險群篩檢，其中包括英國、歐聯(丹麥、瑞典)、紐西蘭等，美國也已開始著手評估其臨床價值，其中英國並已有初步文獻報告刊登於國際癌症雜誌。總結來說，這些論文認為婦女子宮頸癌高危險群篩檢可以降低全國(英國)婦女30%到60%的子宮頸癌罹患機會；英國女性(15歲以上)如果一生只做一次人類乳突狀病毒的高危險群檢驗，則可以降低30%罹患子宮頸癌的機會，如果每五年做一次人類乳突狀病毒的基因檢驗，則可以降低60%得到子宮頸癌的機會。

我們研究小組利用人類乳突狀病毒的檢測，對子宮頸癌的先期研究顯示，人類乳突狀病毒檢查對於子宮頸癌或是子宮頸癌前期的相關性有百分之84，而子宮頸抹片檢查對於子宮頸癌或是子宮頸癌前期的偵測準確率為百分之71，如果合併此兩種檢查，則對於子宮頸癌或是子宮頸癌前期的偵測準確率可以提昇至百分之91，這結果顯示人類乳突狀病毒的檢查，確實可以提高子宮頸癌的早期診斷；近年醫學論文也認為，人類乳突狀病毒的檢驗比同時間多次的反覆抹片更俱有早期診斷的臨床意義，所以在子宮頸抹片檢查的推廣政策下，實施乳突狀病毒檢驗是可以輔助子宮頸抹片檢查，並提高異常子宮頸的檢出率、及降低子宮頸抹片的偽陰性。

人類乳突狀病毒的檢測，除了運用在提高抹片篩檢率、降低偽陰性外，也可以運用在下列幾個方向：

1.對抹片為ASCUS或LSIL的診斷，可以提高正確率與降低偽陽性，如檢測為病毒陽性，則需做陰道鏡切片或進一步的圓錐切片。

2.對做過圓錐切片的病歷，可以運用人類乳突狀病毒的檢測作為復發的預測指標、或作為邊緣是否完整的生化指標。

3.針對做過放射線治療的病患，因抹片判讀常受到放射線影響而不容易判讀，導致許多的偽陽性與偽陰性，因此可以運用人類乳突狀病毒的檢測作為抹片的生化指標。

4.針對高齡婦女的癌症篩檢，人類乳突狀病毒的檢測準確性與子宮頸抹片有同等準確效益。 

Molecular Mechenism of Human Papillommvirus Diseases

Ⅰ.Human papillomavirus:

A DNA tumor virus with a doule-strand close circular DNA genome of 7900 bases. More than 70 types identified with most of them associated with the skun infection andabout 27 types infect the ano-genital mucosa.It encodes 8 genes which express 14 protin products.

Function of HPV transcripts:

E1: act on origin of replication to induce episomal DNA replication.

E2: together with E1 forms origin binding complex. Also a transcription regulator, Particularly a repressor of the E6 promoter.

E4: Act with intermediate filaments of host cell, associate wih viral particle release.

E5a: Anoncoprotein related to the signal transduction of host cell. Act on the ER,  Golgi, related to the endocellular trafficking.

E6: Anoncogene, inactivation of p53 tumor suppresser gene.

E7: An oncogene, inactivation of Rb tumor suppresser gene.

E7 gene alone of either low or high risk HPV transactivate host DNA replication  In the differention of squamouse epithelium.  Differentiation of host cell is required to turn on the E6/E7 promoter and hence Induction of host DNA replication.

L1: External capsid protein of the hexahedral capsid.

L2: Internal capsid protein of the hexahedral capsid.

A productive life cycle of HPV depends on the differention of squamous epithelium. So far it is very difficult to culture HPV. The identification of HPV relies on DNA detection. The weak systemic antigenicity makes serological test both insensitive and nonspecific.

Ⅱ.Human Papillomavirus and Cervical Cancer:

1. Epidemiology:

There are 5000,000 new cases of cervical or anal cancer each year around the world, which are related with the HPV infection. Cervical cancer has been the leading prevalent cancer in Taiwan since 1985.

HPV 16, 18 are related to the development of squamous, adeno-and small cell carcinoma of cervij, avd metastasis of the cervical cancer.

PHYLOGENETIC TREE OF HPV BASED ON AMINO ACID SEQUENCES

About 50-80% of CIN patient have HPV infection, 90% or more human cervical cancers contain HPV DNA. Those remaining HPV(-) cervical cell lines have p53 or RB gene mutation. The most prevalent HPV type in cervical cancer is type 16, folloewd by type 18, 31, 33. In Taiwan and fareast countries, type58, next to type 16 is the second most prevalent type. The prevalence of HPV infection in genital tract is about 25% of female less than 55 years old. The lifelong risk of HPV(+) women to develop cancer is about 3.7%. It usually takes 20 to 50 years.

Patholphysiology:

(A) HPV infection

The primary infection site of HPV is at the squamous-columnar(S-C) junction of Cervical epithelium, where the cells are actively proliferating. The columnar epithelial cells at the S-C junction toeard the endocervix with age. Most cervical cancer occurs at the region between the new and old S-C junctions, which is therefor named “transforming zone”. The original S-C junction of a teenage girl is more exposed at the exocervix and cells within are more vulnerable to HPV infection if she has early sexual exposure. Other estrogen-excess status that leads to cervical extropian and vulnerability include pregnancy and use of oral pills. The way of HPV entry into the epithelium is unknown, probably is through injured (erotic) or inflamatory epithelium and get into the basal (stem) cells.

HPV Transmission

•Cutaneous HPVs are transmitted casually.

•Genital HPVs are transmitted sexually.

Important variables for acquisition:

－ Age at first intercourse

－ Number of sex partners

－ Coincident STDs

－ Immunc status

(B)Integration of HPV DNA into host genome

HPV DNA is usually extrachromosomal in CIN lesions. In malignment lesion Viral DNA is usually found to be integrated. The integration disrupt HPV circular genome at the E2 gene which is a repressor for E6/E7 promoter. This results in an over-expression of E6 and E7 oncogenes. No specificity has been observed for intrachromosomal localizations of HPV integration. One report disclose HPV 16 integrated near the c-src, c-raf and c-myc oncogenes. A small percentage of malignant tumors harbors only nonintegrated copies of viral DNA. The integration is clonal in nature indicating the HPV infection precedes the tumor growth.

The infection of HPV is tissue (i. e. keratinocyte) specific. The abundant AP-1 in Keratinocyte but not fibroblast may be responsible, since there is a crucial AP-1 binding site at the E6 promoter.

(C) E6 and E7 oncogenes

The vast majority of HPV-positive cancer cells express high level of E6 and E7. E6, E7 genes from high risk HPV together are capable of immortalizing primary human keratinocytes, subsequent transfection with v-ras, or after long-time culture, may lead to malignant clones.

Protein products of deregulated E6 and E7 genes bind to tumor repressor gene products,p53 and pRb, and leads to loss of function of these tumor suppressor proteins.p53 and pRb, are also bound to other viral oncoproteins such as E1b (p53) and E1a (pRb) of adenovirus, and large T antigen (both) of SV40 virus.

Expression of the high risk HPVs may lead to aneuploidy (change of chromosome number) and contribute to the other cellular events necessary for a full cancer development.

E7 protein only is sufficient to turn on the DNA replication machinery. E7 binds  

Rb protein, ieading to its sequestration to an inactive form. The pRb normally activate the transfection factor E2F, which is a major machinery to activate the expression of a lot of replication related enzymes and entry into the cell cycle. The major role of E2F is the transcriptional activation of cellular genes that encod proteins important for creating the S phase environment and allowing DNA replication to occur. E6 targeted at the cell cycle check point controlled by p53 which is bound and degraded by E6.

2. Natural history of HPV infection

It generally takes 5 to 10 years for LSIL to progress to HSIL and another 10 to 20 years to invasive Ca. About 1/3 of HPV infection persisted, 1/10 progress to CIN and less than 1/100 ti Ca.

3. Histological Change of HPV infection:

(A) Condyloma acuminata: Papillomatosis, acanthosis with hyperkeratosis, parakeratosis, presence of nuclear atypia and periunclear hals (koilocytosis).

(B)Low grade squamous intraepithelial lesion (LSIL): Aberrant differentiation (mild dysplasia), perinuclear atypia (Koilocytes), absence of abnormal mitotic figure. Comparable to CIN Ⅰ.

(C) High grade squamous intraepithelial lesion (HSIL): Plus the presence of abnormal mitotic figure. Comparable to CIN II,III and CIS.

*Flat cervical condyloma and low grade CIN have the same histology picture.

*Nuclear atycality: enlarged hyperchromatis smudged nuclei, empty or fragmenting nuclei.

*Abnormal mitotic figure: multinucleation, abnormal metaphase, bizarre forms,empty or fragmenting.

III. Perspective of HPV Infection Disease

Other Etiologic Factors of Cervical Carcinogenesis:

Infection of HPVis essential but both insefficient and insufficient for cervical carcinogenesis. In thedevelopment of cancer, it usually takes sij or more “hit” on critical growth control genes (oncogenes or tumor suppresser genes). Infection of HPV leads to inactivation of p53 and Rb, but other etiologic factors are required for the other 4 or more “hits”. Smoking, estrogen and other chronic infections are proven risk factors. All are genotoxic which may lead to genomic instability (or microsatellite instability) and rapid accumulation of genetic hits.