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8

NCCN Guidelines for Patients

®

Mycosis Fungoides, Version 1.2016

What is mycosis fungoides?

Cancer is a disease of cells. Lymphomas are cancers

that start in lymphocytes within the lymphatic system.

There are two main types of lymphomas. Hodgkin

lymphoma is defined by the presence of Reed-

Sternberg or related cells. Non-Hodgkin’s lymphoma

includes all the other types of lymphoma.

Mycosis fungoides is a type of Non-Hodgkin’s

lymphoma. It is a cancer of T-cells. There are many

types of T-cells and thus, many T-cell cancers. T-cells

differ from one another based on the cell’s stage of

development and what job the T-cells have.

Very early forms (precursors) of T-cells are made

in bone marrow. They travel from the marrow to the

thymus to become mature T-cells. When T-cells are

ready to help fight illness, they leave the thymus and

travel to other sites.

Mycosis fungoides starts from T-cells that reside in

the skin but may involve the lymph nodes, blood,

and internal organs. Sézary syndrome is also a T-cell

lymphoma that affects the skin and has very high

numbers of cancer cells in blood. Although related,

research is showing that mycosis fungoides and

Sézary syndrome are not the same cancer.

Inside of cells are coded instructions for building

new cells and controlling how cells behave. These

instructions are called genes. Genes are a part

of DNA (

d

eoxyribo

n

ucleic

a

cid), which is grouped

together into bundles called chromosomes. See

Figure 1.2.

Abnormal changes (mutations) in genes

cause normal T-cells to become cancer cells.

Researchers are still trying to learn what causes

genes to mutate and cause cancer.

Cancer cells don’t behave like normal cells. First, the

mutations cause cancer cells to grow more quickly

and live longer than normal cells. Normal cells grow

and then divide to form new cells when needed.

They also die when old or damaged as shown in

Figure 1.3.

In contrast, cancer cells make new cells

that aren’t needed and don’t die quickly when old or

damaged. Over time, the lymphoma cells may build

up in tissues and may travel in blood or lymph to

other sites. Without treatment, the cancer may cause

organs not to work.

1

Mycosis fungoides basics

What is mycosis fungoides?