Biotech Values

[DewDiligence]

Might you be referring to the lack of predictiveness of EGFr expression level? I have no problem agreeing to that.

The lack of predictive value of the EGFr expression level (which you accept) and the lack of substantial practical value of the test itself (which you do not accept) are two sides of the same coin, no? Saying that the test has little or no practical value is tantamount to saying that an EGFr expression level above the level of detection of the assay does not predict a better response to treatment than an EGFr expression level below the level of detection of the assay.

It only makes sense that if the target EGFr is not there, then anti-EGFr antibody would not work.

However, a negative result on the EGFr screen does not imply that EGFr is not present in the patient’s tumor cells—it merely means that EGFr expression is below the level of detection of the commercial assay.

Note the hurdle for EGFR positivity itself is very low, as described in panitumumab and cetuximab label. We are not even talking about 2+ intensity or >20% cells need to be stained, instead any Parafin tissue block that has 1 out of every 100 cells that's stained would suffice.

This is another way of saying that extremely low levels of EGFr may be sufficient to allow a patient to respond to an anti-EGFr drug, which is consistent with the point I am making about the practical limitations of the commercial assay.

It's surprising and I am sure Dako Cytomation, the manufacture of the EGFr immunohistochemistry testing kit would be unhappy to hear it.

Dako markets the EGFr test because it’s a good business—not because it’s good science. Regards, Dew

p.s. I’ll defer to jbog for sourcing of comments by Dr. Saltz and other “thought leaders” in CRC.