Oncology is the study and treatment of cancer. This is one of the more demanding fields of medicine, and one of the biggest areas of medical research. Careers in this field can be extremely rewarding, but because of the seriousness of the diseases involved, it's not exactly easy work.
Qualification for oncology are based on specializations derived from fundamental medical qualifications. These studies are effectively a medical discipline in themselves, and take several years to complete.
Career advancement in this field is based largely on practice and experience, with qualifications forming the basis of advancement in the important research field. This is one of the few medical disciplines in which research capabilities and resources are almost equal to those of actual clinical practice.
It is not possible to define in any great detail the full scope of possible career progressions. Career advancement in this field is defined by areas of specialization, qualifications and career achievements. Because the medical conditions involved are so complex, it is quite common for career progression to be developed in stages related to areas of specialization. Specializations are themselves progressive, including advanced studies, postgraduate work and participation in research programs.
As you can see, these are actually very high degrees of specialization, and in the course of several years in those fields, the career is defined. The alternative to this process is general practice, which progresses hierarchically within the clinical system, and is a quite different career path.
In this field, general practice is essentially hospital treatment and patient care, which are effectively separate processes from the specialized forms of treatment and care. Although these fields do interact to a point, the actual medical practice is quite different, and usually conducted in specialized facilities.
If you're interested in a career in this field, it is advisable to check thoroughly qualifications and the requirements of career progression well in advance. You'll find that professionals in the field and academic institutions will be provide you with options you may not have even considered.