Purpose: Triple negative breast cancer (TNBC) accounts for approximately 15% of breast cancer cases and is associated with a poor prognosis. In this retrospective study of patients undergoing radiation therapy as part of their treatment, disease-free survival (DFS) and overall survival (OS) of TNBC patients were examined in relation to clinical and treatment-related factors.
Patients and Methods: The electronic records of 214 consecutive TNBC patients treated with surgery followed by radiotherapy at the Mid North Coast Cancer Institute between 2006 and 2016 were reviewed. Overall survival and DFS times were analyzed using the Kaplan-Meier method; multivariate Cox proportional hazard regression modelling was used to assess the significance of prognostic factors.
Results: The majority of tumors were T1 (51.9%), followed by T2 (39.2%) and T3 (6.1%). For the whole group, mean DFS was 106.4 (SD 48.7) months; OS 109.4 (SD 52.1) months. Radiotherapy technique, fractionation protocol and laterality were not significant factors for DFS or OS (p> 0.05). However, compared to breast conservation, mastectomy was associated with poorer DFS (mean 114.2 vs 65.2 months; p< 0.0001) and poorer OS (mean 115.5 vs 80.5 months; p=0.0015). The mastectomy group had fewer patients with tumor size T1 (p=0.001) and higher proportions of T3 (p=0.001) and T4 (p=0.02). On multivariate analysis, tumor size T3/T4 and nodal status N2/N3 were significant factors for reduced DFS (p=0.023 and p=0.0003 respectively). Tumor size T3/T4 was the only significant prognostic factor for reduced OS (p=0.019).
Conclusion: Advanced disease exhibited by tumor size > 5cm and positive nodal status is associated with poorer DFS in TNBC patients. Radiotherapy technique or fractionation protocol were not associated with differences in DFS or OS in our patient cohort.


Keywords: dose fractionation, mastectomy, radiotherapy, survival analysis, triple negative breast neoplasms


PLAIN LANGUAGE SUMMARY

Triple negative breast cancer (TNBC) is an uncommon form of breast cancer that is characterized by a particularly poor prognosis.

In this study we were interested in the clinical and treatment-related factors which influence these patients’ survival. As all 214 patients in our study received radiation therapy, we examined the type of radiation technique used (conventional radiotherapy vs intensity modulated radiotherapy [IMRT]), the number of radiation fractions delivered (conventionally fractionated delivery vs hypofractionated delivery), chemotherapy usage and the type of surgery used (mastectomy vs breast-conserving surgery).

On average, the time between diagnosis and re-appearance of the tumor was 106 months. Overall survival averaged 109 months. Using appropriate (Cox proportional hazard modelling), we found that chemotherapy usage, radiotherapy technique, fractionation protocol and laterality (left vs right breast) were not significant factors for determining disease-free survival nor overall survival (p>0.05). However, larger tumors (>5cm) and nodal involvement were associated with poorer disease-free survival; larger tumors (>5cm) were associated with poorer overall survival. For patients with TNBC, as in other types of breast cancer, early detection provides the best chance of effective treatment.