Hi there,
Dr. Mona Boudreaux has been using that formula longer than anyone else I know. She may have some comments regarding expectations. She's at atthherbs@aol.com.
For myself, if the tumor was quite inflamed, I'd be inclined to use Si Miao San as well. Is Duramax an NSAID (we have one named Deramaxx)? If so, it sounds like you were worried about inflammation. Hoxsey has also been helpful for nasal tumors, too, but we have one plasma cell tumor dog entering his second year who is largely asymptomatic at this point on SMS.
If the tumor was slow growing and not very inflamed, I wouldn't use an anti-inflammatory approach, since deprivation of the blood supply has been shown to convert tumors to malignancy. Instead I would optimize circulation. For that we often use Xue Fu Zhu Yu Tang and Xin Yi San (Magnolia Flower Powder). I find the latter is crucial to the success of these so-called Blood stasis tumors.
Hope fully that gives you some more insight. Tan Yu Tang is more of an anti-inflammatory formula.
All the best,
Steve