Trials of partial mastectomy have shown an incidence of breast recurrence of between 1% and 4% per year, depending on the amount of breast tissue excised and patient selection criteria. Factors associated with an increased ikelihood of breast recurrence include positive surgical margins, ductal carcinoma in situ (DCIS), the presence of lymphovascular invasion and young age of the patient. Borgen et al have published a review of this issue.
Surgical margins, defined as the presence of normal (unaffected) tissue between the tumor and the path of the surgeon’s knife, are important and controversial. Pathologic assessment of tumor margins is often imprecise, however.
Interpreting the literature regarding local recurrence after BCT is complicated by the lack of standardization of margin determination. The NSABP-B06 trial accepted a margin as negative if the cancer was not incised. The Milan trial involved quadrantectomy, with a widely clear margin.
Other studies have considered a 3 mm margin as a clear negative margin. Some retrospective studies have found that positive histologic margins are associated with increased local recurrence, but others have not found this relationship.
Radiation-therapy techniques that boost the tumor bed may compensate for microscopically positive margins, but it is worth noting that the tumoricidal effect of radiation therapy is quite variable. It is our practice to insist upon clear margins, both in DCIS and invasive cancers. Centrally located tumors may be suitable for BCT. To avoid a positive margin at the nipple, BCT may require excision of the nipple/areola complex, but this does not preclude a good cosmetic result. Nipple removal with radiation therapy provides a cosmetic result that is superior to virtually all attempts at breast reconstruction after mastectomy.
Ductal Carcinoma In Situ (DCIS)
The presence of DCIS in and around the invasive tumor has been associated with increased likelihood of breast recurrence. Extensive intraductal component (EIC) is a term used to describe situations in which at least 25% of the primary mass consists of DCIS and in which DCIS is seen in ducts extending beyond the primary tumor. Extensive intraductal component is more common in young patients and is associated with a higher incidence of positive margins and residual tumor in the surrounding grossly normal breast.
Subsequent studies revealed that EIC is likely to represent a margin question and is no longer considered a contraindication to BCT if margins are acceptable. Extensive intraductal component is not radioresistant, nor does it represent a variation of the disease spectrum that must be treated uniformly with mastectomy.