A MD-PhD in Oncology I am about to finish my Bachelor Degree in Computer Engineering and Computational Biology, and planning to apply for a MD-PhD with focus on oncology. After talking to my academic advisers, I had very bad impressions about MD-PhD Program ("such a waste of time", "please just focus on one thing at the time"). However, it seems that such critiques are targeting the general approach of MD-PhD programs, and I still think that for the case of cancer research, it would benefit me a lot to gain the experiences in both.

To that extent, I have one question with two sides: Does earning an MD help improve my research as a PhD (for example, identify more significant and meaningful problems), and does earning a PhD side help me become a more skilled practicing oncologist?
Since you indicated that you are focusing on oncology, it seems likely that a PhD will enhance your oncology practice. This thread on The Student Doctor Network explores the pros and cons of an MD-PhD in Radiation Oncology. The general consensus is that it is worthwhile if you plan to be active in research as an MD, otherwise it may be a waste of time, money, and energy. 

As Shion mentioned in a comment, most MD-PhD's become medical research professors, while it sounds as though you will be in active medical practice. There is a possibility that having a PhD may exclude you from consideration by the hiring boards at non-research-focused institutions. At research-intensive insitutions, the PhD will probably help your case, and certainly can't hurt. It appears that many practicing physicians at top US cancer centers are MD-PhD's. See here, here, and here.