49. A 63-year-old woman presents with a hard, irregular mass in her left breast. Core biopsy shows
malignant ductal cells infiltrating a desmoplastic stroma. Immunohistochemical studies demonstrate
tumor cells that are estrogen receptor (ER)-positive and HER2-negative. Which of the following is the
most likely implication of this receptor profile?

(A) Lack of any predictive value for systemic therapy choices

(B) More aggressive behavior with poor response to hormone therapy

(C) Requirement for anti-HER2 targeted therapy as the main treatment

(D) Favorable prognosis with potential benefit from endocrine therapy