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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
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The most important prognostic factor in carcinoma breast is
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The correct answer is  The Nottingham prognostic index (NPI) is used to determine prognosis following surgery for breast cancer. 
Its value is calculated using three pathological criteria: the size of the lesion; the number of involved lymph nodes; and the grade of a tumour.
Size of the lesion is least important.
The extent of axillary lymph node involvement by breast cancer—is the most established and reliable prognostic factor for subsequent metastatic disease and survival