IIRC, MUC1 is poorly glycosylated in cancer cells as opposed to normal cells. As a result, MUC1 on cancer cells is supposedly more "exposed". But I don't know if this results in higher specificity of Stimuvax.
Note ONTY/Merck would not be the only one jumping on the Mucin bandwagon, there is also Transgene/Novartis.
Back when I was following ONTY more closely I looked at Transgene's TG4010 muc1 vaccine as a comparator. It's different from Stimuvax in that it's a littler longer than a 5 repeat sequence of the core muc1 peptide in a poxvirus delivery vehicle. Redplate posted once that it was to get around the basic muc1 patents that ONTY licensed. Transgene ran a ph II combo trial in stage III/IV NSCLC with similar OS result in terms of ITT missed, but a sub-group was found that was lo and behold stat sig. I haven't followed it since but Transgene was looking to move to ph III.
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