What is Cancer?

1

What is a neoplasm?

A neoplasm, or tumor, is any new mass of cells, where they grow under conditions that normally should not give rise to new cell growth. Benign neoplasms grow, but they do not spread; they disrupt adjacent tissues through mass effect. A malignant neoplasm, or cancer, is composed of cells that invade adjacent tissues and spread. Cancer can spread through lymphatics or through the blood stream (hematologic).

2

What kinds of cancer are there?

Cancers are defined by their tissue of origin. Cancers of epithelial origin, such as skin cancer, tongue cancer, breast cancer, or colon cancer, are called carcinomas. Malignant tumors of mesenchymal origin largely arise from connective tissue and are called sarcomas. Cancers are usually solid groups of cells, but some, like leukemia, are “liquid” tumors. Hematologic malignancies, such as leukemia and lymphoma, are also of mesenchymal origin. Some cancers, like melanoma, arise from cells of the neural crest.

Different types of cancer can arise within a single organ and each may be treated differently. For example, adenocarcinoma, small cell carcinoma, and squamous cell carcinoma all arise within the lung and each is treated differently.

3

Are all cancers life threatening?

Yes. With enough time, every cancer is a fatal disease. However, different cancers progress at different rates. Some cancers, such as adenocarcinoma of the pancreas, are aggressive, difficult to treat, and kill quickly. Other cancers, such as most thyroid and prostate cancers, can be slow growing and often years will pass before patients succumb.

4

How are cancers diagnosed?

Diagnosing cancer requires taking a sample of the tumor for microscopic examination; this is called a biopsy. Several histologic tests are performed. These can include specimen staining, most commonly using a hematoxylin and eosin (H&E) stain. Immunohistochemistry, using an antibody to a protein of interest, can be used to identify proteins found in cancers of a given type. In situ–hybridization DNA can detect DNA sequences of viral origin (e.g., human papilloma virus or Epstein-Barr virus), and gene arrangement studies demonstrate mutations for causing a disease (e.g., the BCR-ABL gene rearrangement is associated with chronic myelogenous leukemia).

5

After diagnosis, what comes next?

After proving the presence of cancer, testing is performed to ascertain the extent of disease—this is called staging. The physical examination may help assess both the primary tumor and nearby lymph node basins. Loss of function can indicate deep tumor spread or tumor invasion of nerve pathways. An enlarged liver may be a sign of hepatic metastases, changes in percussion and auscultation may reflect pleural effusions and obstructing tracheal lesions, and abdominal distention is a sign of ascites or of bowel obstruction. Examination of the primary site (such as the larynx or colon) may require endoscopy.

Nowadays, imaging is almost invariably performed, which may include a computed tomography (CT) scan or magnetic resonance imaging. Functional imaging, such as fluorodeoxyglucose-positron emission tomography, may show lesions that use more sugar than surrounding normal tissues.

6

Why and how are cancers staged?

Cancer staging employs a common language for describing a cancer’s extent, suggests the right treatment for a cancer based on the size and spread of the disease, and may help to predict a patient’s prognosis. Staging is an essential aspect of cancer evaluation and treatment of solid tumors. For almost all cancers, staging employs the tumor, node, and metastasis (TNM) system, where T describes the primary tumor extent, N describes the presence and extent of regional nodal metastases, and M reflects distant metastatic cancer. The TNM categories are combined to assign stages between I and IV, where IV is the most advanced. Most cancers are staged according to the methods described by the American Joint Committee on Cancer in a staging manual (see reference ).

7

How do cells become cancerous?

In a word, mutations. Cancer is a derangement of cells resulting from changes in DNA that alter cellular programming and behavior. When such mutations result in cells that destroy nearby tissues and spread, that is cancer. Mutations in DNA can have effects in many different ways. Mutations in genes can result in loss of function or even gain of function. For example, mutations in the p53 gene resulting in loss of function are seen in a majority of cancers (see reference ). Mutations within promoter regions, splice sites, microRNA, or regulatory elements can all affect cell function. Chromosomal breaks, deletions, and duplications also alter cellular regulation. Mutations may arise spontaneously, be facilitated by inherited genetic variation, result from viral infection, or be caused by carcinogenic agents (including drugs, toxins, and ionizing radiation).