Pathology, Biomarkers, and Molecular Diagnostics
Summary of Key Points
• Biomarker development has profoundly affected basic understanding of carcinogenesis and expanded means of intervention in human cancers. Biomarkers have been applied with variable success in three broad areas that correspond to phases of tumor development and progression: (1) early detection, (2) diagnosis, and (3) prediction of clinical outcome (prognosis) and response to targeted treatment.
• For early detection, biomarkers go through five stages of development: (1) identification of promising directions; (2) validation of a clinical assay; (3) demonstration that the biomarker can detect disease before it is clinically relevant; (4) evaluation of the biomarker during prospective screening; and (5) quantification of the effect of screening on reducing the burden of disease in a population.
• Early detection using quite different approaches has changed the natural history of cervical, colorectal, and lung cancer. Progress depends on improving our understanding of the biology of site-specific carcinogenesis and using intervention strategies informed by basic biology.
• Cancer diagnosis still relies on an evaluation of tumor tissue histology, a complex process associated with interindividual variation; however, new approaches to automated quantitative histologic evaluation and immunohistochemical analyses are under active development.
• New molecular diagnostic approaches that utilize assessment of quantitative messenger RNA signatures, fluorescent-in-situ hybridization, quantitation of microRNAs, and genetic sequencing can now be accomplished with accurate use of formalin-fixed paraffin-embedded tissues.
• Molecular testing can provide guidance in prioritizing therapies for patients most likely to benefit and can identify patients who have been proven not to benefit from a targeted therapy.
• Molecular testing can also provide clinicians with a rationale to guide specific patients toward specific clinical trials.
• As new molecular techniques have been applied to cancer diagnosis and treatment, the necessity of developing standardized processing approaches for solid tumor specimens has been appreciated and has helped to change tissue collection and specimen-handling routines.
1. Recent reduction in mortality from cervical cancer is attributed to:
A Herpes papillomavirus (HPV) testing using Digene technology
2. Adenomatous polyposis coli (APC) mutation contributes to:
3. Which of the following interventions has resulted in the greatest reduction in mortality from specific tumor types?
A Resection of small invasive lung tumors detected by computed tomography
B Ablation of dysplastic cells detected by cervical Papanicolaou smear
C Excision of malignancies detected by fecal occult blood testing
4. Targeted therapy relies on:
A Hematoxylin and eosin sections for detection of treatable tumors
B Low-dose computed tomography imaging
C Mutational testing to identify activating mutation and gene rearrangements
5. Which of the following DNA sequence testing depends on nucleotide chain termination chemistry?
6. KRAS mutations in colon carcinoma:
A May be associated with resistance to epidermal growth factor receptor (EGFR) blockade by monoclonal antibody depending on the site of mutation in DNA coding sequences
B Are the sole driver mutations in colon carcinoma
C Are all equally effective in conferring resistance to EGFR blockade by monoclonal antibody
7. The activating change(s) in EML4-ALK rearrangement in lung carcinoma is (are):
1. Answer: C. Although several methods are now available for identifying the causative agent of cervical carcinoma (HPV), mortality reduction has preceded the introduction of these methods into clinical practice and is largely attributable to detection by cytologic examination and ablation of preinvasive cervical dysplasia. However, screening methods are rapidly evolving. The greater sensitivity of the molecular methods to detect HPV infection and the longer interval that is acceptable between screenings for HPV suggest that HPV testing may play a more prominent role in cervical carcinoma screening in the near future.
2. Answer: D. APC is involved early in sporadic colon carcinogenesis, as well has in familial adenomatous polyposis (FAP). APC mutation is a prominent component in many colon cancer screening platforms.
3. Answer: B. The ablation of premalignant epithelium prior to the development of invasive carcinoma results in the greatest reduction of mortality through early detection.
4. Answer: E. Effective treatment with targeted agents is a two-step process in which adequate, properly diagnosed tumor tissue is obtained and mutational testing is performed on the identified tumor cells. Obtaining adequate tissue for appropriate testing can be a limitation in the selection of appropriate targeted agents for the treatment of solid tumors.
5. Answer: E. The nucleotide chain termination chemistry for DNA sequencing is highly versatile and can be applied in many different platforms, including NexGen and Sanger sequencing (see text for fuller explanation).
6. Answer: A. Mutations in codon 12 are the most common KRAS mutations in colon carcinoma and are most commonly associated with resistance to EGFR blockade. Recently, other sites, most notably codon 13 (p.G13D), have been found to be less resistant to anti-EGFR monoclonal antibody treatment.
7. Answer: B. Although translocations are frequent in lung cancer, EML4-ALK is one of the few consistent translocations identified in lung carcinoma. The juxtaposition of EML4 promoter and ALK tyrosine kinase domain results in a high level of expression of ALK and activation of intracellular signaling pathways. EML4 is only one of numerous fusion partners of ALK, and all translocation variants are most readily detected by FISH technology at the present time. This example illustrates the diversity of molecular changes that may be drivers and treatment targets in lung cancer and the multiple platforms currently needed to detect them.
