ALTERNATIVE MULTIVARIATE MODELING FOR TIME TO LOCAL RECURRENCE FOR BREAST-CANCER PATIENTS RECEIVING A LUMPECTOMY ALONE

Certain prognostic factors (patient and/or tumour characteristics) may be associated with low (or high) risk for local recurrence. Patients with these characteristics could be candidates for less (or more) adju vant therapy or a less (or more) aggressive surgical approach. However , the assessment of many factors can be problematic with the standard multivariate technique-a Cox proportional hazards model and step-wise regression. We compared the results obtained when using a Cox model wi th those from four alternative models (exponential, Weibull, log logis tic and log Normal) in step-wise and all subset regressions. Between 1 977 and 1986, 293 primary invasive breast cancer patients were treated at the Henrietta Banting Breast Centre with a lumpectomy with or with out an axillary dissection, and with no postoperative adjuvant therapy . The variables considered were age, lymph node status, tumour size, e strogen receptor (ER), progesterone receptor (PgR), histologic grade, nuclear grade, carcinoma in situ (CIS), amount of CIS, and presence of tumour emboli. With follow-up to 1991, nodal status was not found to be included in the step-wise Cox model, although it was in the step-wi se exponential, Weibull and log Normal models, and in the best all sub set models for all model types. The variables tumour emboli, ER, age, CIS and nodal status were consistently included in the best all subset regressions, regardless of model type. In the 1993 follow-up, the var iables in the stepwise Cox model were tumour emboli, ER, age, CIS and nodal status. The multivariate consideration of all possible subsets o f regression variables led to an earlier indication of the importance of nodal status, while the data strongly supported accelerated failure time models over the Cox model.