It is understood that Fleishman-Hillard, the incumbent, has declined the opportunity to repitch, although its medical education arm, The Remedy, will continue to handle med ed for the brand.
An agency shortlist is thought to have already been agreed, with an appointment likely in April.
Aromasin, an irreversible type 1 aromatase inhibitor, is marketed for the treatment of advanced breast cancer in post-menopausal women whose tumours no longer respond to the gold-standard tamoxifen.
Data from a Pfizer-sponsored study last year showed post-menopausal breast cancer patients who switched from tamoxifen to Aromasin had a significantly reduced chance of recurrence and increased disease-free survival compared to patients who remained on tamoxifen.
AstraZeneca, which makes rival product Arimidex, has argued that Pfizer's study simply shows the aromatase inhibitor class of drugs is better at preventing the recurrence of breast cancer than tamoxifen.
Pfizer filed supplemental submissions in Europe and US for approval for Aromasin in early breast cancer treatment last December.
Pfizer is also considering bringing in agency backing later this year to handle UK med ed for colorectal cancer brand Campto and both PR and med ed for Sutent - a pre-launch treatment for patients with metastatic renal-cell carcinoma and gastrointestinal stromal tumours.
It is understood that pitches for Campto and Sutent are yet to be scheduled and that the current agency review is solely for Aromasin.
Interaction Marketing and PR continues to handle PR for Campto. Its contract is not under review.