IHC methods for tumor cell detection have been applied widely to preparations of cells from bone marrow, lymph node aspirates, and peripheral blood mononuclear cells. Cells can be smeared or centrifuged by cytospin onto slides, or sections taken from frozen or formalin-fixed, paraffin-embedded tissue. IHC is performed using standardized methods. Slides can be scanned by eye, though to achieve a high level of sensitivity, thousands to millions of cells must be screened, which is tedious and time-consuming. Thus, image analysis has become a popular approach for screening.7 Alternatively, flow cytometry has been utilized to achieve high number and rapid cell analysis.8
Tumor cells also can be assessed using DNA or RNA targets. Genomic targets can be utilized, if available, for the detection of a particular type of tumor. DNA targets have the advantage of greater stability compared to mRNA transcripts and, unlike protein targets, can be amplified to obtain greater analytic sensitivity. Some types of solid tumors do possess chromosomal translocations or point mutations that can be utilized for early diagnosis or detection of residual disease. Examples include certain sarcomas characterized by specific translocations, or KRAS mutations common in pancreatic and colorectal carcinoma, which have been used for detection of cells in pancreatic fluid and stool, respectively.912 Microsatellite markers have been employed to assess cancer in certain body fluids.13,14 However, for most cancers, such tumor-specific targets are lacking, and thus mRNA expression unique to the cell of origin for the tumor must be utilized.
For this purpose, RT-PCR has been widely used for detection of occult tumor cells in a variety of sample types. This approach permits analysis of a large number of cells simultaneously, and with great analytical sensitivity owing to the use of nucleic acid amplification. Key to the success of this approach is the careful choice of the mRNA target and meticulous design of the assay. Since few, if any, tumor-cell-specific mRNA targets exist, target transcripts that are unique to the tissue, such as cytokeratin for epithelial cells or PSA for prostate cancers, generally are used. In some cases, enrichment of tumor cells via immunoselection can enhance both the sensitivity and specificity of the RT-PCR assay.15,16 Amplification approaches other than PCR also can be utilized effectively.17
Some investigators have targeted free nucleic acids in serum or plasma, rather than in the cellular fraction. Both DNA and RNA exist free in the circulation and have been studied in patients with breast cancer, melanoma, and colon cancer.14,18-20
Was this article helpful?
Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.