Association Between Different Molecular Subtypes Of Breast Cancer And Risk Of Second Primary Contralateral Breast Cancer

Objective We all know that breast cancer patients have an increased risk of developing second contralateral breast cancer,especially those with HR-negative.However,the association between different molecular subtypes of breast cancer(luminal A,luminal B,HER2-overexpressing,basal-like)and the second primary contralateral breast cancer is not clear.Therefore,we used the SEER database to explore the risk of second contralateral breast cancer according to different molecular types.Methods There were 56,385 patients diagnosed with first primary breast cancer,of whom 1,223 developed second primary contralateral breast cancer from the SEER 18 database(2010-2015).Standardized incidence ratio(SIR)was calculated as the ratio of the observed numbers of second primary contralateral breast cancers among breast cancer survivors to the expected cases in the general population.Data were classified by latency periods,race,age at diagnosis,and calendar year of breast cancer diagnosis.Results The overall risk of second primary contralateral breast cancer in the three molecular subtypes of breast cancer was reduced(HR+/HER2-(SIR=0.76#,95%CI: 0.71-0.81),HR+/HER2+(SIR=0.76#,95%CI: 0.62-0.91),HR-/HER2+(SIR=0.91,95%CI:0.69-1.17))except basal-like breast cancer(SIR=1.34,95%CI:1.17-1.53).In the luminal A groups,SIR was statistically significantly increased among patients age 20-29,the SIR was still increaed for the patients whose age younger than 50.Prominently,for all latency periods and race,the basal-like groups had the highest risk of developing second breast cancer in all groups.We also found that patients with age at the diagnosis 30-39 have a higher risk than the other groups regardless of ER/PR/Her2 status,except for patients with age at the diagnosis 30-39 in the luminal A group.Conclusion: HR-/HER2 breast cancer not only has a poor prognosis,but also is more likely to develop second primary contralateral breast cancer compared with the other breast cancer molecular subtypes.Emphasis on screening frequency may be necessary for breast cancer survivors diagnosed at 30-39,and for the HR+/HER2 population may need to take preventive measures earlier.