What does "which" refer to?

Context:

The biggest effect was in women over 50 with hormone-sensitive breat cancers. Their risk of dying from breast cancer during the follow-up was 14% lower than similar women with similar cancers who had mastectomy.

The researchers did not investigate the reasons behind these results, and the question why women appear to fare better with lumpectomy and radiation as opposed to mastectomy, which more seem to be going for, remains to be answered.

One concern women have when choosing a treatment option, is whether their cancer will recur, and the perception that this is less likely following mastectomy, may influence their choice.Jan 31 2013 13:48:11Regular Member813Joined Oct 05 2007 11:10:11High mind turns the grace of the universe as the glory of your life.