To cite items from Oncology Abstracts, please make sure you include the names of the authors, year of publication, abstract title and, most importantly, the fact that it is from Oncology Abstracts, with volume and abstract number. You may also wish to include the name of the conference.
For example:
Nother A 2017 Thyroid Disorders After Oncologic Treatment in Children. Presented at Society for Endocrinology BES 2017, Harrogate, UK. Oncology Abstracts 1 S9