Background: The prognosis of patients with T1 breast carcinoma remains controversial. Some studies have shown a low risk of lymph node metastasis and distant failure whereas others have not, possibly due to differences in the definition of tumor size. In this study, the authors assessed the relation between macroscopic tumor size, microscopic invasive tumor size, axillary lymph node involvement, and prognosis in a group of patients with clinically lymph node negative disease.

Methods: Between 1968 and 1986, 1865 women with American Joint Committee on Cancer clinical Stage I or II infiltrating carcinoma of the breast were treated at the Joint Center for Radiation Therapy with conservative surgery and radiation therapy. The study population was limited to 118 patients with clinically negative axillary lymph nodes for whom the macroscopic pathologic tumor size was identified unambiguously as being < or = 2.0 cm, who underwent an axillary lymph node dissection with at least 6 lymph nodes sampled, and for whom the microscopic size of the invasive component could be determined. The median follow-up time for surviving patients was 134 months (range, 90-208 months). No patients with pathologically negative axillary lymph nodes received systemic therapy.

Results: Macroscopic and microscopic tumor sizes differed by > 5 mm in 17 patients (14%), by 3-5 mm in 24 patients (20%), and by < or = 2 mm in 77 patients (65%). The macroscopic tumor size was smaller than the microscopic size in 37 patients (31%), larger in 55 patients (47%), and equal in 26 patients (22%). Pathologic axillary lymph node involvement was present in 21% of all patients. The risk of lymph node involvement was not significantly different for those patients with tumors < or = 1 cm compared with patients with tumors > or = 1.1 cm, regardless of whether tumor size was measured by macroscopic or microscopic examination. The 10-year actuarial rate of freedom from distant recurrence (FFDR) was 91% for lymph node negative patients with macroscopic tumors measuring < or = 1.0 cm compared with 77% for patients with macroscopic tumors measuring > or = 1.1 cm (P = 0.07). When measured microscopically, the rates were 96% and 72%, respectively (P = 0.001).

Conclusions: There often is a discrepancy between microscopic tumor size and macroscopic tumor size. T1 tumors have a substantial risk of axillary lymph node metastasis whether measured macroscopically or microscopically. Among those patients with pathologic lymph node negative tumors who are not treated with systemic adjuvant therapy, microscopic invasive tumor size is a better predictor of 10-year FFDR than macroscopic tumor size. There is a substantial risk of distant failure for patients with tumors whose invasive component microscopically measure > or = 1.1 cm, whereas the prognosis for patients with tumors that microscopically measured < or = 1 cm is excellent. These results suggest that the microscopic size of the invasive component of breast carcinomas < or = 2.0 cm routinely should be reported.