JAK-2 or CALR?

In the olden days, before the discovery of the JAK-2 genetic mutation, the only way to diagnose ET was by process of elimination of underlying causes for an elevated platelet count. And even though JAK-2 tests may run false negatives (25 percent of the time, according to my hematologist), a positive JAK-2 helps your doctor initiate treatment and monitoring quicker.

But JAK-2 isn't the only mutation associated with ET.

Last year, Blood Journal reported a study of ET patients with two different types of genetic mutations, JAK2 and CALR (calreticulin). The bottom line for us patients is that those with the CALR genetic mutation seem to have a much lower thrombosis risk than those with the JAK2 mutation. That's signicant info given that the greatest risk for ET patients is clotting.

Here's more:

Those with JAK2 mutation were generally older (median age of 50) and female (64 percent of the patients studied). They also showed ...

• Slightly higher hemoglobin and white blood counts
• Lower platelet counts (median of about 700)
• More spleen enlargement (6.4 percent)
• Risk of ET morphing into polycythemia vera (PCV) was 29 percent after 15 years
• More thrombosis at time of diagnosis (33 percent)

Those with CALR mutation were younger patients (median age of 45) and more likely to be male (51 percent of those studied). They also showed ...

• Slightly lower hemoglobin and white blood counts
• Higher platelet counts (median 880)
• Less spleen enlargement (2.4 percent)
• No risk of ET morphing into PCV
• Less thrombosis at time of diagnosis (5 percent)

If you read the lists carefully you saw the irony: Even though those with CALR have higher platelet counts, their risk for clots is lower. So your risks for getting sicker with ET involve more than just your platelet count.

Because JAK2 is found in some ET and PCV patients, researchers believe that those two diseases are closely linked, perhaps JAK2-ET being a kind of pre-PCV condition. However, CALR-ET seems to be a completely separate disease.

I looked through my online medical chart and couldn't find that I had been tested for CALR. But I will be asking my hematologist about this at my next appointment.

Anyone had the CALR test? As I understand it, treatment for both JAK-2 and CALR types of ET are the same, but CALR-ET patients may have a better prognosis.

UPDATE: There is some chatter about the CALR gene over at the Cancer Compass. See link at right.

Be well!

Two 2015 studies about JAK-2 and CALR forms of ET
Read more about my JAK-2 test

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