Introduction

This chapter is designed for readers who have little or no prior knowledge of tumors. It summarizes in plain English the main, fundamental topics in the other chapters, excluding Chapter 10. The sections of the chapter are in the same order as the chapters in the book. Thus Section 1.1 summarizes Chapters 1–3. Section 1.2 summarizes Chapters 4–7. Section 1.3 summarizes Chapters 8 and 9. Section 1.4 summarizes Chapters 11–13. Section 1.5 summarizes Chapter 14.

Keywords

Tumors; causation; molecular pathology; micro-metastases; clinical features; treatments

Outline

Tumors are autonomously growing accumulations of cells which occur in types characterized by distinct, variable combinations of variable differences from their respective kinds of cell of origin. The natures and causes of most of the types of tumors are not well understood. The types which invade adjacent tissues and metastasize to other parts of the body are liable to cause death if untreated.

This chapter summarizes the fundamental aspects of tumors as a basis for the discussions of topics in the following chapters. Much of the material will be at familiar to medical students, as well as to many bioscience students in disciplines such as molecular biology, cell biology, and genetics.

The general principles of normal histology which are relevant to tumors are outlined in Appendix 1. The general aspects of the human genome are described in Appendix 2.

1.1 Essential Aspects of the Nature, Types, and Rates of Incidence of Tumors

1.1.1 “Tumors” Used in the Sense of “True” Tumors

In its most general sense, a “tumor” is any swelling in the body. The term can be applied to a wide variety of conditions including physiological swellings such as a normal pregnant uterus, as well as to pathological swellings such as inflammations (see Section 11.1). In this book, as in most medical situations, the term “tumor” is used as a synonym for “neoplasm” or “true tumor.”

All tumor cells are irreversibly modified normal cells. As a result, tumor cells have two sorts of hereditary characteristics [1]:

Tumor cells usually have the following characteristics:

The degrees of retention of parental features and the degrees of intensity of the acquired abnormalities are highly variable between different tumors. The variability is seen at three levels: between different types of tumors, between different cases of the same kind of tumor, and between different foci in individual cases of tumor.

While the distinction between tumors and nontumorous lesions is usually easy, pathologists recognize many clinicopathological conditions as “tumor-like.” Examples include benign hyperplasias of the breast and prostate gland.

1.1.2 Classifications and Terminology of the Tumor Types

Tumors comprise a thousand or so different types. How these types are recognized and the differences between them are described in multivolume works such as the Armed Forces Institute of Pathology’s Atlas of Tumor Pathology [2] and the World Health Organization Classification of Tumours [3]. The diversity of the tumor types also applies to their clinical behavior and responses to therapies. This is the basis of the complexities which are apparent in clinical oncology [4–7].

The different types of tumors are classified according to three main criteria: