Chapter 3: Principles of Cancer Risk Assessment and Genetic Counseling

INTRODUCTION

It is estimated that ~5% to 10% of all cancers are hereditary, meaning that they developed largely as a result of a germline mutation in a cancer predisposition gene. Rapidly evolving genetic technology is increasingly allowing for tailored cancer therapy, screening, and risk reduction for individuals with an inherited cancer predisposition. Essential steps in ensuring the realization of the promise of personalized medicine include appropriate risk assessment, development of a management plan, patient education, and facilitation of patient coping. This chapter describes the essential elements of the traditional process of cancer genetic counseling and risk assessment, including the intake and collection of personal and family medical history, risk assessment, informed consent, genetic testing, and psychosocial assessment. However, the field of hereditary cancer genetic counseling and testing has changed significantly over the past decade with rapidly increasing demand and concerns about access to genetic counseling and testing. This changing landscape has led to the proposal and implementation of various alternative care delivery models which often preserve at least some of the elements of the traditional process yet may utilize a differing order, importance, delivery method, and providers of these elements. Identified barriers to access, as well as some alternative care delivery models, will also be introduced in this chapter.

SPORADIC, FAMILIAL, AND HEREDITARY CANCER

All cancer is considered to be a genetic process, as it is due to genetic changes that accumulate in the deoxyribonucleic acid (DNA) of an individual throughout their lifetime and alter the way the cells grow and divide. However, genetic changes causing an increased risk for certain cancers can also be inherited from parent to child if these changes are present in the germ cells (i.e., egg and sperm) of a parent. When an individual inherits a nonfunctioning (also known as “mutated”) copy of a gene related to hereditary cancer, that individual is at an increased risk throughout their lifetime for developing cancer. It is estimated that 5% to 10% of cancer is due to a specific inherited genetic cause.¹ In general, cancer falls into three specific categories: sporadic cancer, familial cancer, and hereditary cancer.

The majority of cancer occurs sporadically. Sporadic cancer occurs when there are genetic mutations that accumulate in the DNA of an individual over time. This occurs due to random chance, lifestyle choices, and certain environmental factors and is not due to an inherited genetic mutation. Families with sporadic cancer will generally have cancers at the typical age of onset with no apparent pattern of inheritance. For these individuals, it is very unlikely that genetic testing will reveal a genetic mutation that will explain the personal and/or family history of cancer. Sporadic cancer occurs due to a combination of both modifiable and nonmodifiable risk factors. Examples of nonmodifiable risk factors include aging, ethnicity, and gender; examples of modifiable risk factors include alcohol and tobacco use, physical inactivity, and occupational exposures,²