How Tumors Grow and Mastitis
Comments on how a tumor develops and Metastasizes (how cancer spreads to other parts of the body).C. Norman Coleman, MD
Director, Radiation Oncology Sciences Program
National Cancer Institute
Robert Weinberg, PhD
Daniel K. Ludwig Professor for Cancer Research
Massachusetts Institute of Technology
NORMAN COLEMAN, MD
Cancer is an entity where cells proliferate beyond normal control, so they grow to too big a mass, and they behave erratically so they'll go to other parts of the body. It's basically cellular proliferation out of control.
NORMAN COLEMAN, MD
The harm of that is you can get huge masses that can destroy local tissue and you can get huge volumes of disease, so your entire metabolism gets affected.
ROBERT WEINBERG, PhD
The growth of a tumor is a series of multiple sequential steps and in fact most human tumors take 40, 50, 60 years to develop, explaining why cancer is primarily a disease of older people. The fact is that a normal cell goes through a whole series of evolutionary steps before it develops into a cancer cell. The first change it may show is it may begin to multiply abnormally creating a number of cells that otherwise appear fully normal under the microscope. The next thing that may happen is that these cells begin to lose their shape and may appear to look a little more like cancer cells. Subsequently they may begin to disrupt normal tissue architecture and create shapes in the tissue which are very unfamiliar to someone who examines the tissue, the normal tissue, under the microscope. And finally these cells may begin to invade into normal adjacent tissue and so they may progress from a benign state, where they're localized, to an invasive state where they may begin to infiltrate into neighboring tissue. Ultimately cells that are invasive may also metastasize and cause new tumor sites throughout the body so this is a very complex sequence of multiple steps that results in an evolutionary process that occurs over 30, 40, 50 years. With luck many of these evolutionary processes will not reach their conclusion in our bodies by the time we reach 60, 70, 80 years of age.
ROBERT WEINBERG, PhD
Large masses of cancer cells, which we call tumors, kill people in different ways. A cancer may grow locally and press on adjacent local tissues and compromise their functioning. Often a cancer can grow in the abdomen for a period of years without our even noticing it simply because the abdomen is rather flexible and you don't really notice the pressure created by the tumor. In the brain, however, there it's surrounded by the skull and there if a tumor begins to grow then sooner or later it's going to compress some of the brainy tissue. Ninety percent of cancer patients, however, don't die because of the primary tumor that arises in one place and expands there. Instead, ninety percent of cancer patients are actually killed by metastases, that is to say, groups of cancer cells that leave the primary tumor, travel to a distant site in the body, and there begin to colonize a new tissue and form therein a new tumor mass. It's these metastases which more often than not lead to the death of the patient. Often by compromising the function of the lung or the brain or even eroding bones.
ROBERT WEINBERG, PhD
The fact is that that program of invasion and metastasis is extraordinarily inefficient, and we imagine that only one out of a million cells leaving a primary tumor succeeds in forming a metastasis at a distant site.
ROBERT WEINBERG, PhD
Until recently we knew an awful lot about how cells form a primary tumor and almost nothing at the molecular level about how they succeed in colonizing distant tissues, the processes of invasion and metastasis. This colonization is actually a very complicated process because a cancer cell growing in a primary tumor must invade into adjacent tissues, find access into a blood vessel, travel through the blood vessel to a distant tissue, and in that distant tissue escape from the blood vessel, invade into the distant tissue and therein begin a program of colonization to form a new tumor mass
ROBERT WEINBERG, PhD
Still, we need to know how all that happens and why it's so inefficient. And we're beginning to learn how that happens, by studying, interestingly enough, early steps in the development of an embryo. The fact is that, as an early embryo develops--and here I'm not only talking about human embryos, I'm talking about frog embryos and worm embryos and fly embryos--when these early embryos develop, cells migrate from one part of the embryo to another and engage in many of the behaviors that we associate with metastasizing cancer cells. How do cancer cells learn how to invade and metastasize? They don't invent these behaviors; instead they resort and revert back to the behaviors of their ancestors in the early embryo who already exhibited these behaviors in a well-defined program. And so cancer cells are very opportunistic, they take advantage of these early embryonic behaviors in order to acquire for themselves the ability to invade and to metastasize.