Number of techniques have been developed and
introduced in the field of oncology for diagnosis and treatment of tumor cells.
Polymerase Chain Reaction has added much to the scientific advancement, so is its
role in cancer diagnosis. PCR techniques like nested PCR, q-PCR, real time PCR etc.
are frequently being used in cancer diagnosis and treatment methods. This technique
is most useful in breast and lung cancer diagnosis along with other cancer types.
Digital PCR technique is thought to be very useful technique in breast cancer screening.
It is also used for detection and quantification of tumor cells in body.
Cancer diagnosis, PCR, q-PCR, RT-PCR, tumor cells diagnosis,
PCR is basically a process in which small molecules
like DNA particles or proteins etc are amplified in a cyclic process which
generates a large number of copies. In the same manner this technique can be
used for the diagnosis of cancer (1). PCR was invented by Kari Mullis in 1985
which was developed with the passage of time and is now used for the detection
of cancer cells such as for detecting malignant cells in lymph nodes or blood. RT-PCR
has been used for the detection of neoplastic cells in lymph nodes or blood in
case of leukemia, neuroblastoma, melanoma, prostate cancer and blood cancer
The site of origin of metastatic tumors can be
identified objectively using RT-PCR assay which involves 92 genes (3). The use
of polymerase chain reaction has increased the ability to study genetic
material and its related issues more clearly. Now, other than research purposes
PCR technology is also used in diagnosis of certain diseases like AIDS,
hepatitis and cancer etc (4).
Previously diagnosis of breast cancer in labs was
carried out in most of the hospitals using traditional methods of cell
culturing and direct hormone receptor assay and these methods required much
time and money. Later attention was directed towards the use of RT-PCR where
HER4 oncogenes were expressed using this technique. This technique has also
been used for the early diagnosis of breast cancer (5). RT-PCR is also a
sensitive tool used to monitor minimal residual disorder in leukemia patients.
This is done by the amplification of fusion gene transcript (6). Another method
used for cancer diagnosis is the analysis of plasma miRNA (microRNA) by quantitative
PCR. But analyzing the small quantities of miRNA is quiet challenging with this
(7). Real time PCR is replacing traditional PCR technology rapidly and
advancements are being continuously made in field of diagnosis (8). Digital PCR
has also been used for quantifying the exact copy number of two lung-cancer
related miRNAs in 35 patients having lung cancer and 40 controls (9).
RT-PCR is also considered to be an excellent tool for
detection of circulating tumor cells in peripheral blood and bone marrow of
cancer patients (10). RT-PCR is generally thought to be limited to small
amounts of samples. It can also be scaled up to represent the expression of 192
genes at a time (11). In PCR based diagnosis rare mutations in body cells are
usually diagnosed and detected like in k-ras
genes, p53 or other genes. It is observed that mutant and normal genes are
amplified at nearly equal efficiency (12).
In order to check the involvement of miRNAs in lung
cancer carcinogens miRNAs expression profile was examined. This differentiated
cancerous cells from non-cancerous ones. This was confirmed using RT-PCR
technology. Lung cancer is one of the leading causes of deaths due to cancer in
world (13). Lymph node metastasis in head and neck can be detected using an
automated q-RT-PCR assay with high accuracy. Moreover combined q RT-PCR and SNB
could guide surgical treatments more appropriately concerning patients with
head and neck cancer (14).
Another type called crystal digital PCR proved to be
a good technique to monitor mutational status in cfDNA’s plasma. In addition it
also proved to be a good technique for detection of known mutations as compared
to MPS in case of features like time to results (15). Much of the work has been
done on RT-PCR and lung cancer relation. A real time PCR can detect four genes
simultaneously, which was developed and tested on specimens of lung cancer
(16). The utility of multiplex d-PCR was investigated for seven most common
mutations in codon number 12 and 13 0f the KRAS oncogene derived from plasma
samples of those patients having metastatic colorectal cancer. This revealed
that 19 patient tumors carried KRAS mutations (17).
The efficiency of different types of PCR was also
tested by comparing the sensitivity of conventional PCR, quantitative PCR,
nested PCR along with western blots meant for detection of prostate cancer
tumor markers by the use of prostate cancer cells. As a result it was found
that nested PCR technique generates results quickly as compared to real time
PCR (18). PCR technique is very useful in predicting treatment response,
detection of treatment failure which is linked with acquired drug resistance
and monitoring disease progression (19). Another type called multiplex digital
PCR allows detection of tumor DNA circulating in cells. Moreover pico-droplet
PCR technology aids in simultaneous screening of the same sample for several
other mutations (20).
Although it is a sensitive process concerning
molecular genetic tests, PCR is a very reliable, relatively easy and low cost
method used for diagnosis of certain diseases including cancer. RT-PCR is a
process used to find or detect small amounts of RNA and it can also be used for
classifying cancer. As it is well understood that this technique is used to
extend and increase the copy number of very small pieces of DNA, RNA and
proteins etc so it is well suited for the diagnosis of mutations in cells and
cancer detection. RT-PCR is being used for tumor profiling in labs. Previously
some traditional methods were used for diagnosis and treatment of cancer but
the use of this technique in oncology has made the task much easier.
Along with diagnosis quantitation of gene expression
and tumor causing mutations is also of great importance. This is necessary for
investigation of gene patterns which are responsible for cancer development. So
for all this PCR is a very reliable method and q-PCR particularly. Several
other techniques have also been introduced but PCR is well founded technique.