Detection of human papilloma virus (HPV) and K-ras mutations in ...

1092 NOUTSOU et al: HPV AND K-ras IN LUNG CARCINOMA
logical factors. In the current study we confirm the presence
of HPV in lung carcinomas, using primers from both the E6 and
LI ORFs. The use of primers located in the E6 ORF, which
remains intact in the case of high risk HPV type integration
into the host genome, allows better diagnostic sensitivity. No
difference was found in the detection rate of the virus using
the two sets of primers from the E6 and LI ORFs.
It is noteworthy that HPV was also detected in cases of
adenocarcinoma. Recently, there has been increasing interest
in the association between HPV and glandular neoplasia. In
many studies HPV DNA has been found in adenocarcinomas
and adenosquamous carcinomas as frequently as in squamous
cell carcinomas of the cervix (39-41).
In our study we found that multiple subtypes of HPV may be
related to lung cancer. However HPV 18 was the predominant
type, which is in agreement with other studies reporting that
high-risk HPV types were more frequently detected (19,20,22).
Their identification in both squamous cell carcinomas and
adenocarcinomas as well as in adenosquamous and undifferentiated
large cell carcinomas suggests a key role in the
process of lung carcinogenesis. Moreover, it has been suggested
that infection with high risk HPVs could serve as a prognostic
indicator of malignant progression in lung squamous cell
papillomas (22).
Multiple molecular changes have also been documented
in lung cancer. These include activation of dominant oncogenes,
such as the ras gene family (23), myc and HER-2/new
genes, as well as loss of recessive growth regulatory genes,
or onco-suppressor genes (p53, rb) (23,26).
Several studies have reported an incidence of 15-33% of
activated K-ras gene in lung carcinomas, while more recent
studies have revealed a higher incidence of more than 50%
(42-44). In the current study we found K-ras codon 12 point
mutations in 18% of the specimens examined. In cases of
squamous cell carcinomas the incidence of K-ras mutations
was higher than in other studies (24,42), propably due to the
more sensitive assay used. Activation of the K-ras gene was
examined, since point mutations of this member of the ras
family are found more commonly in lung cancer and occur
predominantly at codon 12.
It has been suggested that K-ras mutations arise predominantly
at the non-invasive stage of lung carcinogenesis,
and may be associated with the transformation of dysplastic
cells to neoplastic (45). Moreover, detection of K-ras mutations
in sputum may precede diagnosis of lung cancer (29). On the
other hand, a significant number of lung adenocarcinomas
harbor ras mutations in only a small percentage of the cancer
cells, indicating that K-ras mutations represent a late event in
lung carcinogenesis (23). This concept is consistent with the
association of ras mutations with increased tumor growth and
invasiveness, as suggested by the poorer prognosis of mutationpositive
than mutation-negative cases treated by surgical
resection (44,46). We found an association between K-ras
mutations and the stage of the tumor, occuring more frequently
at cases with stage III. However, no correlation was found
between K-ras mutations and the clinical outcome of the
patients examined. In 50% of the HPV-positive cases, K-ras
mutation co-existed. This might suggest that HPV infection
is not sufficient by itself for malignant transformation, but
requires co-operation of an activated ras gene. In addition,
carcinogen exposure may induce transformation in several
fields of the bronchial epithelium through the induction of
different genetic changes.
Our results indicate that HPV infection and K-ras gene
activation may play a role in a subset of lung tumors. The
possibility of synergic mechanisms between HPV, ras gene
mutations and chemical or physical carcinogens such as cigarette
smoking should also be considered.
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