I was diagnosed with breast cancer in November 2007, at the time was doing Iyengar yoga three times a week. Spoke to Iyengar teacher who said that it was not a good idea to do Iyengar till given the all clear, as ? whether Iyengar increased cell division, thereby accelerating the cancer division. Obviously made me very nervous about returning to Iyengar, but miss it very much, nearly completed treatment, keen to return to study of Yoga. Anybody got any suggestions about dilemma.

I've never heard this before and would take it with a grain of salt. I would highly recommend you talk to your MD about this issue, asking him/her when you can begin to take yoga again and what types of exercises / movements are okay for your condition.

From my understanding of yoga and cancer and from the studies I've read, yoga would only be beneficial in the recovery of breast cancer. Please check out the following links for more info on this:
http://www.nytimes.com/2008/08/14/health/nutrition/14fitness.html?ref=health
http://www.foxnews.com/story/0,2933,198115,00.html
http://www.cbsnews.com/stories/2008/03/10/health/webmd/main3921381.shtml

But going back to your previous Iyengar instructor may not be a good idea, and I would recommend you find a teacher that is supportive of your recovery with breast cancer.

thank you for replying so promptly, I found the articles really helpful. I will look around for other Iyengar teachers I think. Thanks again

As someone who is trained to work with cancer patients, I agree with Timothy. I see no reason you could not do Yoga during your recovery and I would advocate you do it unless your physician has advised against it. If you have other questions or concers .. my trainer is here: http://www.thecancerspecialist.com/ and she is fabulous. she has been through cancer and designed exercise for cancer patients.
but you want people who support you. if this instructor does not, you could get a new one or educate the instructor. maybe the instructor is unsure of how to handle your case.