How the Nottingham Prognostic Index Estimates Breast Cancer Recurrence Risk
The Nottingham Prognostic Index (NPI) is a well-established, published prognostic formula developed at Nottingham City Hospital and validated across decades of breast cancer outcome data. It combines three findings that a pathologist reports after surgery — the size of the tumor, whether cancer has spread to nearby lymph nodes, and how abnormal the tumor cells look under a microscope (grade) — into a single score. That score sorts patients into good, moderate, or poor prognostic groups, which historically correlate with the likelihood of relapse and breast-cancer-specific survival over time. This calculator applies the classic NPI formula so you can see how those three pathology values combine, and what group they fall into using the original published cutoffs.
How the calculation works
The formula is NPI = (0.2 × tumor size in cm) + N + G. Tumor size is the largest diameter of the invasive tumor in centimeters. N is the nodal stage, scored as 1 if no axillary lymph nodes contain cancer, 2 if one to three nodes are involved, and 3 if four or more nodes are involved. G is the histologic tumor grade (1, 2, or 3) assigned by a pathologist based on how closely the cancer cells resemble normal breast tissue. Adding these three components together, with tumor size scaled down by a factor of 0.2, produces a single index typically ranging from about 2 to 9.
What the prognostic groups mean
Using the classic NPI cutoffs from the original Nottingham/Galea cohorts: a score of 3.4 or below places you in the Good Prognostic Group, historically associated with roughly 80% 15-year breast-cancer-specific survival; a score above 3.4 up to 5.4 is the Moderate Prognostic Group, historically around 42%; and a score above 5.4 is the Poor Prognostic Group, historically around 13%. These figures come from older treatment-era cohorts — modern surgery, radiation, endocrine therapy, and chemotherapy generally produce meaningfully better outcomes than these historical numbers suggest, so treat the percentages as a relative prognostic signal, not a current survival guarantee.
What the NPI does not capture
The NPI does not include estrogen or progesterone receptor status (ER/PR), HER2 status, Ki-67 proliferation index, patient age, or lymphovascular invasion, all of which modern oncologists weigh alongside it. It also predates gene-expression assays such as Oncotype DX and MammaPrint, which many treatment teams now use to estimate distant-recurrence risk and guide chemotherapy decisions in early-stage, hormone-receptor-positive disease. Use this calculator to understand how the classic NPI formula works and where your pathology values fall — not as a replacement for staging, receptor testing, genomic assays, or your oncology team's individualized assessment.