• Vincent Vinh-Hung, Tomasz Burzykowski, Jan Van de Steene, Mia Voordeckers, Jan Lamote, and Guy Storme.
• Oncology Center, Academic Hospital, Vrije Universiteit Brussels, Jette, Belgium. conrvhgv@az.vub.ac.be
• Tumori. 2005 Jan 1; 91 (1): 9-14.

PurposeTo identify subgroup effects that might influence the survival results of postoperative radiotherapy.Patients And MethodsWomen selected from the Surveillance, Epidemiology, and End Results database, aged 40-69 years, with non-metastasized T1-T2 breast carcinoma, in whom axillary lymph node dissection was performed. Subgroup analyses were performed using proportional hazards models with interactions. Joint significance of subgroups was evaluated with the Wald test. Event was death from any cause.ResultsStatistically significant interactions were found between type of surgery (breast-conserving [BCS] or mastectomy [ME]), radiotherapy [RT], T stage, and extent of nodal involvement, but not between treatments and nodal examination. For each treatment combination, ME-no RT, ME+RT, BCS-no RT, BCS+RT, the mortality hazard ratios were respectively: 1, 1.12, 1.11, 0.78 in T1, 0-3 positive nodes; 2.45, 2.77, 2.71, 1.92 in T2, 4+ nodes; 1.31, 1.38, 1.33, 1.19 in T2, 0-3+ nodes; and 3.41, 2.79, 3.44, 2.40 in T2, 4+ nodes. The corresponding joint tests showed: in the absence of radiotherapy, no significant survival disadvantage for breast-conserving surgery vs mastectomy; with radiotherapy, significant survival advantage for breast-conserving surgery irrespective of stage and for mastectomy in T2, 4+ nodes. For mastectomy in less advanced stages receiving radiotherapy, excess breast cancer deaths suggested undocumented adverse selection. The corresponding result was considered inconclusive.ConclusionsThe analyses found subgroup effects that should be taken into account to interpret treatment results in breast cancer.

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