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Wednesday, April 18, 2007

Burkitt's Lymphoma is High Yield for the USMLE Step 1

Burkitt Lymphoma
a form of non-Hodgkin's lymphoma

Associated with Epstein Barr Virus and is commonly located in the jaw of Africans (the classic patient)

Classic Translocation = t(8;14) which moves the c-myc gene on chromosome 8 right next to the Immunoglobulin (Ig) Heavy Chain.

Here is a joke for you. I hope you find it hilarious. Okay, a giggle will do. Tell it to someone else, embrace the awkwardness that ensues and that should tattoo it to your brain for a while.

How come Mick ate one for?

-----Here is what the joke really means----
come Mick = c-myc
ate = 8 - since c-myc is on chromosome 8
one = 1
for = 4

To get heavy!
heavy = Ig Heavy chain which is on chromosome 14

And here's a little doodle to drive it on home:

That big guy there is Mick (myc) who has just ate (8) one (1). For (4) what? To get heavy.
c-myc is on chromosome 8
Ig Heavy chain is on chromosome 14

Believe me, this joke is much funnier if you're telling it to yourself when you are looking at a question on it.

Here is what some practice questions I've seen ask and is mentioned in various review therefore I made sure I knew this for my exam although I had to look it up again for this post.

The function of c-myc: c-myc is a proto-oncogene which codes a protein that regulates nuclear transcription. When it is moved next to the gene for the Ig heavy chain it becomes constantly active since the body is constantly making Ig heavy chains. At this point it is now called an oncogene. c-myc now causes the B-cells to constantly reproduce themselves over and over again. This results in a high grade lymphoma

This is in contrast to B-cell follicular lymphomas in which BCL-2 (a gene which promotes apoptosis). When BCL-2, a tumor suppressor gene, is translocated it becomes functionally inactive and so B-cells can't undergo apoptosis the same anymore. This is an example of low grade tumor.

So I think this is how you should think about it: Burkitt's lymphoma is when B-cells actively divide whereas in B-cell follicular lymphomas, B-cells don't die.

Also, here's the classic"Starry Sky Appearance"

I just want to point out here what that refers to. The dark purple areas are really just a bunch of neoplastic B-cells that are dividing much more rapidly now that c-myc is always active. ("Dark is Dividing") The stars are the lighter areas which are much fewer in number - these are the macrophages. I'm not sure what they are doing there, but I do know that they are NOT the problem. Perhaps they are trying to help out in getting rid of the tumor.

That's what I think is really important for this tumor that seems to be a pretty hot topic for the exam.


Anonymous said...

You are doing a great job and thank you for sharing your thoughts.

UB said...

hey mike.. i thought BCL 2 was the fountain of youth gene, and it inhibits apoptosis.

Anonymous said...

You were right on the reason for the "starry sky" appearance...since there is increased mitotic rate of B cells there is also increased cell death; leading to macrophage ingestion of surrounding dead cells. This leaves an empty space and therefore a white spot on a black background.

Anonymous said...

ub .... Bcl-2 is the prototype anti-apoptotic protein. High levels of Bcl-2 prevent apoptosis. Thus, when Bcl-2 is overexpressed cells cant undergo apoptosis.

Adel said...

When BCL-2, a tumor suppressor gene, is translocated it becomes functionally overexpressed so B-cells can't undergo apoptosis anymore.

Niamh said...

c-myc: upregulated in burkits lymphoma because it stands for C MY Chin ....... same as RET .... upregulated in multiple endocrine neoplasia because its a Really Endocrine Tumour ....

Mike Birkhead said...

The RET is clever, but I fail to see how "see my chin" (C MyC) helps you remember "burkit" ?