A 48-year-old woman from Delhi undergoes modified radical mastectomy and axillary lymph node dissection for a 3.5 cm invasive lobular carcinoma of the left breast. Final histopathology shows: tumour size 3.5 cm, grade II (Nottingham 5/9), 4 of 12 axillary nodes involved (levels I and II), no extranodal extension, negative margins, and negative sentinel node in level III. Oestrogen and progesterone receptors are positive; HER2 is negative. Staging imaging (chest X-ray, abdominal ultrasound, bone scan) is normal. What is the TNM stage and most appropriate adjuvant therapy?