Why the existence of invaded resection margins in the conservative treatment for breast cancer?

The presence of invaded margins at histopathological paraffin examination, after a conservative treatment of breast cancer, is the main factor of local recurrence; this situation imposes a reintervention with new resection margins.
The consequence is the increase of hospitalization days for this pathology, the increase of costs, the delay in initiating the adjuvant therapy, the decrease of cosmetic quality of surgery, and an important emotional and psychological impact upon the patient. In this study we tried to identify a series of factors in favour of the resection margins invasion, factors depending on the patient or on the surgical technique. For this purpose we retrospectively assessed the data of 98 patients operated in the Coltea Surgery Clinic, from January 2011 to December 2014, for whom the initial indication was conservative treatment for in situ or invasive mammary neoplasm. The assessment of resection margins during surgery through the extemporaneous histopathological examination was provided for all 98 patients, 55 of which presented resection margins free of cancer cells. The others 43 presented one or more invaded margins, imposing re-excisions during the surgery, or mastectomy if the final cosmetic result would have been unfavourable.
We chose conservative treatment for 21 patients and mastectomy for 22 patients. Other 5 patients were added to the last group after we found discordance between the extemporaneous and the paraffin examination, 4 of the group which has not needed re-excision and one from the group which needed primary excision. In the end, we had two groups, one of 51 patients who did not need reexcision, and another of 47 patients who needed margin resections during primary surgery or mastectomy (primary or secondary to the paraffin examination). The two groups were compared depending on the age, tumour size, histological type and depending on the distance between the tumour and the resection margin. The statistic analysis of the two groups did not reveal significant differences as to the age of patients and the size of the main tumour. But, depending on the histological type, the association between the invasive and in situ component showed an increase in the relative risk of invaded margin of 2.17 times.
We also found an increase in the relative risk when the distance between the tumour and the resection margin was smaller than 1 cm; in this case we obtained a value of 2.09 times. In this respect, we consider that during the conservative treatment of breast cancer, the macroscopic assessment of resection margins, especially of the distance to the primary tumour is not enough to ensure a free margin. Another method has to be associated in order to have a more exact detection of the invasion or of its absence in the resection margin, fact which would allow the enhancement of oncological and cosmetic results of the procedure.