Breast Cancer in Thyroid Cancer Patients, can One lead to Another?

Aims: To demonstrate the increased risk of developing a second primary thyroid or breast cancer in patients with prior breast or thyroid cancer and to study the clinicopathological characteristic of breast cancer (B2) as a secondary malignancy following a diagnosis of thyroid cancer (T1) or thyroid cancer (T2) following a diagnosis of breast cancer (B1) to find a common aetiology. Study Design:  Retrospective cohort study Place and Duration of Study: Breast & Endocrine Surgery Unit, Surgery Department Hospital Putrajaya between January 2008 and December 2018. Methodology: Data of patients with breast cancer as first primary malignancy and thyroid cancers as second primary malignancy, and vice versa, between January 2008 to December 2018 was extracted using electronic search through the hospital information system database and compared for their tumor’s histological type, size, hormonal status (ER/PR), presence of locoregional lymph node and distant metastasis. We also examine any history of radiotherapy for first primary breast cancer patients and history of radioactive iodine ablation for first primary thyroid cancer. Results: 1.1% (n:4) of T1 develops B2 while 0.5% (n:8) of B1 develops T2 but we are unable to demonstrate a significant correlation between hormonal status of the tumour, radioiodine ablation or radiation therapy and the risk of developing second primary malignancy. Conclusion: There is an increased risk of thyroid cancer as a secondary malignancy following breast cancer and an increased risk of breast cancer as a secondary malignancy following thyroid cancer. No common aetiology can be demonstrated from this study.