Running off so don't have time for a more involved response. Basically, yes this can be done. There are a spectrum of surg onc fellowships, some that are more research heavy than others. In addition, if you are getting some papers in, it demonstrates your willingness to work and your ability to juggle research and clinical duties, a good thing that will serve you in fellowship and into the future.
The traditional route is to take some time off for research, but if your program doesn't offer a great experience, you may be just as well off getting a few papers in and going straight through and selling yourself on potential, as taking a chance that yhou will have a terrible research experience and make your app looking even worse with a few unproductive years. There is no minimum number of papers, but having something is important to differentiate yourself.
