| Background & objective: Breast cancer is the most common malignancy in women worldwide,and incidence is increasing year by year.With the increasing maturity of medical technology and people’s self-care awareness,breast cancer was detected earlier than ever,especially those small breast cancer<1cm.The most of small breast cancer were always in the early stage,lymph metastasis and distant metastasis were rare,and the prognosis was not bad.Clinical guidelines lack specific adjuvant chemotherapy for small breast cancers without lymph metastasis and there is widespread controversy.The proposal of the concept of “precision medicine” has led scholars to look forward to exploring the treatment of this population from technologies such as large data and genomics,more accurate individualized treatment,therefore it is of great significance to use clinical data to objectively evaluate the effect and prognosis of chemotherapy.To provide more reasonable choice of postoperative adjuvant chemotherapy for small breast cancer patients,to avoid undertreatment and overtreatment.Methods: From the US National Cancer Institute’s SEER(Surveillance,Epidemiology,and End Results)database,clinical data of 35024 eligible female patients from 2012 to 2014 were selected,comparative analysis of the benefit of adjuvant chemotherapy for tumors of different sizes.Study endpoint was overall breast cancer survival(OS),and Cox proportional hazards regression model was used for univariate analysis and multivariate analysis analysis for the effects of adjuvant chemotherapy on the four subtypes of T1 a and T1 b and the difference in prognosis.In order to eliminate confounding factors that may bais the results,using Propensity Score Matching(PSM)method to verify the results,finally,Kaplan-Meier method was used to draw the survival curves,P value less than 0.05 is considered statistically significant.Results: A total of 35024 female patients were included in the SEER database,10073(28.8%)with T1 a stage,and 24951(71.2%)with T1 b stage in this study.The proportion of histology grades I and II was relatively concentrated,which were 14638(33.43%)and15171(45.87%),respectively.The number of patients who choose breast-conserving surgery is the largest,with 24142(66.57%),the proportion of patients who did not receive postoperative adjuvant chemotherapy and postoperative adjuvant radiotherapy was larger,which were 30528(79.71%)and 20976(57.94%),the age of onset mostly after 60 years old,with 20878(58.23%),compared with the other groups,the absolute proportion of HR+/HER2-subtypes accounted for 29288(81.44%)among the four molecular types.COX multivariate results showed that in the four groups of patients with molecular subtypes of stage T1 a,HR+/HER-,HR+/HER2+,HR-/HER2+,and HR-/HER2-,there was no significant statistical difference in overall survival between the chemotherapy group and the non-chemotherapy group(p= 0.11,p=0.36,p=0.22,p=0.20),respectively.In the T1 b HR+/HER2-group,the overall survival of the chemotherapy group and the non-chemotherapy group also showed no significant statistical difference(p=0.67),however,in the molecular subtypes of HR+/HER2+,HR-/HER2+,and HR-/HER2-,there were statistically significant differences in the overall survival of the chemotherapy group and the non-chemotherapy group(p< 0.0001,p=0.01,p< 0.0001),respectively.After PSM,a total of 842 pairs(1684 cases)of patients in stage T1 a were matched,and 2757 pairs(5514 cases)of patients in stage were matched,and differences in the baseline data of the paired group were not significant.The COX proportional regression risk model was used to perform multivariate survival analysis,the results showed that among the four molecular subtypes in T1 a,there was no significant statistical difference in overall survival between the chemotherapy group and the non-chemotherapy group(p= 0.3,p=0.1,p=0.27,p=0.48),respectively,after PSM,there was no significant statistical difference in overall survival between the chemotherapy group and the non-chemotherapy group in HR+/HER2-of T1b(p=0.74),but,in the molecular subtypes of HR+/HER2+,HR-/HER2+,and HR-/HER2-,there were statistically significant differences in the overall survival of the chemotherapy group and the non-chemotherapy group(p= 0.0007,p=0.01,p=0.0002).Kaplan-Meier survival curve showed that there was no statistical difference in overall survival between the chemotherapy group and non-chemotherapy group in T1a(p=0.88),also in the HR+/HER2-subgroup of T1b(p=0.053),in the molecular subtypes of HR+/HER2+,HR-/HER2+,and HR-/HER2-,there were statistically significant differences in the overall survival of the chemotherapy group and the non-chemotherapy group(p=0.0104,p<0.0001,p<0.0001).Conclusion:(1)In the absence of lymph node and distant metastasis,chemotherapy has no effect on the prognosis of patients with T1 a,and this part of patients can be exempted from adjuvant chemotherapy.(2)In the absence of lymph node and distant metastasis,chemotherapy can not improve the prognosis of patients in HR+/HER2-in T1 b,nevertheless,it can significantly improve the prognosis of with HR+/HER2+,HR-/HER2+,and HR-/HER2-,thus it is suggested that all molecular subtypes should undergo postoperative adjuvant chemotherapy except HR+/HER2-patients. |
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