LIMITATIONS OF TRADITIONAL CANCER DIAGNOSTIC AND PROFILING APPROACHES
Cancer is difficult to diagnose and manage due to its heterogeneity at morphologic, genetic and clinical levels. Traditional methods of diagnosis for solid tumors which are routinely used as the initial step in cancer detection involve a tissue biopsy followed by a pathologist examining a thin slice of potentially cancerous tissue under a microscope. A recently obtained tissue sample is used in combination with chemical staining techniques to enable analysis of the biopsy. After staining, the pathologist determines through visual inspection whether the biopsy contains normal or cancerous cells, with those that are deemed cancerous being graded on a level of aggressiveness. Often an analysis of biomarkers relevant to that tumor type is also performed on the tissue, ranging from immunohistochemistry to mutation analysis by various means such as microarrays and DNA sequencing. After the diagnosis, a clinical workup is performed according to established guidelines for the specific cancer type. From there, the physician determines the stage of progression of the cancer based on a series of clinical measures, such as size, grade, metastasis rates, symptoms and patient history, and decides on a treatment plan that may include surgery, watchful waiting, radiation, chemotherapy, or stem cell transplant.
This type of analysis is dependent on the availability of a recently obtained tissue biopsy for the pathologist to analyze. Such a biopsy is often not available. A tumor may not be readily accessible for biopsy, a patient’s condition may be such that a biopsy is not advised, and for routine periodic patient monitoring to evaluate potential progression or recurrence, a biopsy is a fairly invasive procedure and not typically performed. As the length of time between when the original biopsy, diagnosis or surgery is conducted to the current evaluation of the patient increases, the likelihood that an original biopsy specimen is truly representative of the current disease condition declines, as does the usefulness of the original biopsy for making treatment decisions. This risk intensifies in situations where a drug therapy is being administered, because the drug can put selective pressure on the tumor cells to adapt and change.
Similarly, the heterogeneity referred to above means that different parts or areas of the same tumor can have different molecular features or properties. In evaluating a biopsy specimen, the pathologist will take a few thin slices of the tumor for microscopic review rather than exhaustively analyzing the whole tumor mass. The pathologist can only report on the tumor sections analyzed and if other parts of the tumor have different features, such as biomarkers corresponding to specific treatments, they can be missed. A more representative analysis of the entire tumor, as well as any metastases if they are present, is very helpful.
Thus, excisional biopsies provide only a snapshot in time of some of the rapid, dynamic genetic changes occurring in tumors. In addition, excisional biopsies are invasive, can’t be used repeatedly, and are ineffective in understanding the dynamics of tumor progression and metastasis.
On the other hand, liquid biopsy, or blood-sample tests can generate actionable information for oncologists by analyzing CTCs that are continuously shed by tumors into the bloodstream. Highly sensitive analysis of individual CTCs have demonstrated a high level of heterogeneity seen at the single cell level for both protein expression and protein localization and the CTCs reflected both the primary biopsy and the changes seen in the metastatic sites. By detecting and quantifying genomic alterations in CTCs, liquid biopsy can provide real-time information on the stage of tumor progression, treatment effectiveness, and cancer metastasis risk. This technological development is making it possible to diagnose and manage cancer from repeated blood tests rather than from a traditional biopsy.