if you lookat those under a microscopeunder very high power, and you're looking at just a single lobule and a duct, you'llsee that the lobules and ducts are linedby a single layer of cells, and if welook at this even closer, you'll see thatthere's a dot in the middleevery single one of those cells. So, thatis the cell nucleus, or the controlcenter of the cell. That nucleus containsall of the DNA and information thatinstructs the cell on how to behave,when to grow, and when to die. So, normalcell growth would be that a cell wouldget a signal to grow; at some point, thecell would be instructed to copy itselfor replicate itself, and during thisprocess, all of the DNA is copied, andthen once a successful cell has beencopied, the original cell is signaled todie, okay, and that is very regulated, andit's a normal process in cell growth,such that these cells are constantlyturning over, but as long as they'rebehaving appropriately, by and large,there will be a single layer of cells. So,what happens in a cancer cell? In acancer cell, there is a problem.
There'sdamage to the DNA, okay. We don't alwaysknow why the DNA damage occurs--it couldbe because of a carcinogen or anexternal influence, it could be becauseof a genetic predisposition in the cellitself, but whatever the reason, if thisDNA damage is not caught, a cell can bemade with mutated instructions, okay. Sothe nucleus of the cell now has DNAthat's not going to give theinstructions that the cell needs to growproperly, and instead, it's going to tellthe cell to grow and divide too fast, ornot listen to the normal cell, the signalto undergo cell death, and what thatcauses is uncontrolled growth. So thecell is now being told to replicate andgrow, and each time it replicates, it'sgoing to replicate the same mutated copyof itself. Now, when the cancer cells are stuck inthe duct--as in you see in this picture,the cancer cells are growing, and they'remultiplying, but they're stuck in theduct--we call this ductal carcinoma in-situ, or stage zero breast cancer. At thisstage,
the cells may form a mass or alocal problem, but they don't have theability to spread outside the duct. So, aninvasive cancer, which is what we'reconcentrating the webinar on today, thecancer cells have learned to get outsideof the duct, and the reason why this isimportant is because just outside of themilk duct in the fatty and supporttissue of the breast is also where theblood vessels and lymphatics live, andthese cancer cells could be carried awayby the lymphatics and the blood vesselsto other areas of the body, and this isthe danger of breast cancer. So, if thebreast cancer cells stayed in thebreast, they may cause a mass, they maycause a local problem, but they wouldnever take your life. The danger to yourlife becomes when these cancer cellslearn to leave the breast and go toplaces that you need to live, like yourliver or your lungs. So, when we plan yourtreatment, and when we think about yourprognosis, we're going to think aboutyour tumor stage, and we do that bywhat's called TNM staging. So, T--what isthe size of the tumor in your breast, N--has a tumor traveled to nearby lymphnodes, and if so, how many, and then M--thisis metastases, or travel to distant sites,and this is when the cancer is spread todistant organs, such as your liver oryour lungs, and we call this stage IVbreast cancer. The other thing that we'regoing to think about when we planyour treatment, and that is very highlyassociated with your prognosis, issomething called your biology of yourbreast cancer, and this is a veryimportant concept to understand, andbasically, it's when we look at yourcancer cells under the microscope, and wetry to learn about how they're behavingand what's driving their growth. So, weknow they're not listening to normalgrowth signals, they're growing too fast,but how abnormal are they behaving? Andwe're going to look at two things. We'regoing to look at tumor grade andtumor biomarkers. So, tumor grade issaying how abnormal does a cell lookunder the microscope, okay, we grade itI, II, and III. In grade I, we seethe cell looks abnormal,
but it lookspretty much still like a normalbreast cell. These are not veryaggressive. They tend to grow slowly, andthey're less likely to spread. Now, on theconverse, grade III looks more abnormalunder the microscope, and these are moreaggressive cancers that tend to growmore quickly and are more likely tospread. Grade II is intermediate, and this isthe most common type of breast cancerthat we see. The other thing we're goingto look at is tumor biomarkers. Tumorbiomarkers are proteins that areexpressed by the tumor cells that informus about what is driving their growth,and it can also direct treatments,so we will look at your cancer cellfor 3 proteins--the estrogenreceptor, the progesterone receptor, andHER2 overexpression. So, if we look at allthe breast cancer cases we see in theUS, about 60% to 65% will behormone positive, and we'll just groupthat and say estrogen positive. And about20% to 25% will be HER2-neuoverexpressing, and the remaining 16% to18% is something we call triplenegative, so they don't express thehormone receptor, and theyare not overexpressing the HER2 protein.So, let's go into a little bit moredetail about each kind--eachof these subtypes. So, estrogenreceptor positive, again, is the mostcommon type of breast cancer. What thatmeans is that your cancer cell isexpressing the estrogen receptor, andthat means that estrogen, which normallyfloats around in your body, can bind tothis receptor, and it's signaling thecancer cell to grow. Think of it likeestrogen is feeding your cancer cell.This also means we can block estrogen,either by blocking the estrogen in the bodyor blocking the estrogen receptor, and wecan starve the cancer sell, and that can be an effectiveway we can treat estrogen receptorpositive breast cancer.
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