MRCS-1471

A 37 year old woman has recently undergone a mastectomy along with axillary node clearance for an invasive ductal carcinoma. Histological analysis show a completely excised grade III lesion measuring 3.5cm. Two of the axillary nodes are significant for metastatic spread. The tumour is found to be oestrogen receptor negative. Which of the following would be the next best step in the management of this patient?