HER2 Support Group Forums - View Single Post - Please post your two cents on Herceptin "side effects" real or perceived!

Lani · 09-23-2006, 05:50 AM

Herceptin is 99% humanized but there is still 1% of mouse antigens in it. Perhaps you are reacting to the mouse antigens as foreign invaders (which they are!)

At the Genentech stockholders meeting (I am not one, but attended with a friend who is) this year I asked if people had developed antibodies to Herceptin monoclonal antibodies (as such a phenomenon had been described with another monoclonal antibody being used for either rheumatoid arthritis or leukemia--I don't remember which at this moment, but can look up--which had altered its efficacy obviously in some)

The CEO of Genentech said it had not been described with Herceptin and because it was 99%humanized--although the antibody is "manufactured" or "cloned" within a mouse, what is being made by the mouse has 99%
" human" content--people had not reacted to that 1% of mouse.

I do not think they have had many cases of allergic reactions to the first dose to investigate. Of course, once someone has a bad reaction you don't want to keep giving it to them (at least not without some good premedications) and challenging their immune systems to provoke some life-threatening reaction in order to study it. I hope they can find some way around that and find out exactly what has caused you to react this way so you can benefit from herceptin. The good news is, from what I can gather from reading, lapatinib is a totally different kind of compound (not a monoclonal antibody, no mouse content, much smaller moledule) and should not cause a simiilar reaction. Herceptin can stay in your body up to six months after the last infusion. While this is not good in terms of your adverse reaction, perhaps it will give you some protection until lapatinib becomes available. I would also think they might be more willing to give you lapatinib once approved off label as you had shown yourself not resistant to Herceptin but allergic to herceptin and thus without an equivalent alternative. The FDA asked for fast track approval of lapatinib this week--hopefully it will take four months or so (wishful thinking!) if good reports come out at San Antonio. I don't know how Canada approves drugs, but perhaps GSK's compassionate use program could be of help.

I obviously have no expertise in this area (have merely educated myself by reading a lot of articles), but I hope something I have written has given you some idea to pursue or ask about, put your mind a little at ease or helped you in some way.

Best of luck!

09-23-2006, 05:50 AM	#81
Lani Senior Member Join Date: Mar 2006 Posts: 4,778	from what I understand Herceptin is 99% humanized but there is still 1% of mouse antigens in it. Perhaps you are reacting to the mouse antigens as foreign invaders (which they are!) At the Genentech stockholders meeting (I am not one, but attended with a friend who is) this year I asked if people had developed antibodies to Herceptin monoclonal antibodies (as such a phenomenon had been described with another monoclonal antibody being used for either rheumatoid arthritis or leukemia--I don't remember which at this moment, but can look up--which had altered its efficacy obviously in some) The CEO of Genentech said it had not been described with Herceptin and because it was 99%humanized--although the antibody is "manufactured" or "cloned" within a mouse, what is being made by the mouse has 99% " human" content--people had not reacted to that 1% of mouse. I do not think they have had many cases of allergic reactions to the first dose to investigate. Of course, once someone has a bad reaction you don't want to keep giving it to them (at least not without some good premedications) and challenging their immune systems to provoke some life-threatening reaction in order to study it. I hope they can find some way around that and find out exactly what has caused you to react this way so you can benefit from herceptin. The good news is, from what I can gather from reading, lapatinib is a totally different kind of compound (not a monoclonal antibody, no mouse content, much smaller moledule) and should not cause a simiilar reaction. Herceptin can stay in your body up to six months after the last infusion. While this is not good in terms of your adverse reaction, perhaps it will give you some protection until lapatinib becomes available. I would also think they might be more willing to give you lapatinib once approved off label as you had shown yourself not resistant to Herceptin but allergic to herceptin and thus without an equivalent alternative. The FDA asked for fast track approval of lapatinib this week--hopefully it will take four months or so (wishful thinking!) if good reports come out at San Antonio. I don't know how Canada approves drugs, but perhaps GSK's compassionate use program could be of help. I obviously have no expertise in this area (have merely educated myself by reading a lot of articles), but I hope something I have written has given you some idea to pursue or ask about, put your mind a little at ease or helped you in some way. Best of luck!