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Cancer

How Cancers Are Different

In spite of the similarities shared by all cancers, cancer acts differently and responds differently to treatment depending on where it occurs. The organ or tissue in which cancer develops affects how tumors act, and how tumors act influences how they need to be treated.

All malignancies can be divided into two major groups: on the one hand there are the leukemias, lymphomas, and myelomas; on the other there are malignancies of the other organs and tissue of the body. These are collectively known as solid tumors. The fundamental differences between solid tumors and malignancies of the blood include the nature of the genetic damage in each.

Leukemias occur in bone-marrow cells that give rise to blood cells, and when those cells become malignant, they circulate in the blood where they can be readily detected. These malignant cells also often produce substances that suppress development of normal bone marrow cells. These substances may also suppress responses to infection, which is a major concern during the treatment of leukemia and an important cause of death in these patients.

 

 

Leukemias and lymphomas also often show characteristic damage to their chromosomes. These cytogenetic changes help oncologists determine the type of leukemia or lymphoma a particular patient has, and the optimal treatment for that patient. (insert link here to additional information when available.)

Differences in cytogenetic abnormalities and other genetic damage make each of the 20 or 30 types of leukemia act like different diseases

Furthermore, even when leukemias in two patients involve the same type of cell and even though the cells from each may look the same under the microscope, the type of disease the patients have can be as different as identical twins with opposing personalities.

Leukemia cells from patient A might look exactly like those from patient B, and will both be called leukemia. But the classification of leukemia is no longer based solely on the visible; it is based on cytogenetic and molecular changes as well.

If cytogenetic tests are done to reveal such differences, cells from the first patient might show a problem involving chromosomes 9 and 22, an abnormality known as the 9;22 translocation. Analysis of the identical-looking leukemia cells from the second patient, however, could show an abnormality involving chromosomes 8 and 21, the 8;21 translocation.

The difference between the two is significant: The type of leukemia involving the 8;21 translocation is exquisitely sensitive to the standard treatment for leukemia. Ninety percent of these patients go into remission. Leukemia that involves the 9;22 translocation, on the other hand, is exquisitely resistant to the same drugs; only 5 to 10 percent of these patients go into long-term remission.

We call both diseases 'leukemia,' but they involve completely different genetics that are not susceptible to the same drugs. They use different biochemical pathways.

Such differences in genetic damage probably explain why 78 percent of children with leukemia are curable compared to only about 40 percent of adults. The two groups represent completely different diseases. A child of two who develops acute lymphoblastic leukemia (ALL), for example, has nearly a 90 percent chance of being cured, but an adult over 60 who develops what appears to be the same disease-ALL-has about a 25 percent chance of long-term survival.

It's the exact opposite. It's a different disease hiding in the same cell; it's a different disease at the molecular level. Sometimes we know what those molecular differences are, as in the case of the 9;22 and the 8;21 translocations, and in some cases we don't know yet.

This article originally appeared in Frontiers (Autumn 1998) a chronicle of cancer programs at The Ohio State University and was adapted for use on NetWellness with permission, 2004.

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Last Reviewed: Feb 21, 2005

Darrell E Ward, MS Darrell E Ward, MS
Associate Director
Cancer Communications
Wexner Medical Center
The Ohio State University

Robert W Brueggemeier, PhD Robert W Brueggemeier, PhD
Dean/Professor, Pharmacy Central Business Office
College of Pharmacy
The Ohio State University

Michael A Caligiuri, MD Michael A Caligiuri, MD
Professor of Hematology
Professor of Molecular Virology, Immunology, & Medical Genetics
College of Medicine
The Ohio State University

Reinhard A Gahbauer, MD Reinhard A Gahbauer, MD
Former Professor
The James
The Ohio State University

Eric H Kraut, MD Eric H Kraut, MD
Professor of Hematology
College of Medicine
The Ohio State University