WHEN LIGHTNING STRIKES TWICE: A CASE OF METACHRONOUS INVASIVE BREAST CARCINOMA AND PAPILLARY THYROID CARCINOMA IN A FEMALE FILIPINO PATIENT

Abstract

INTRODUCTION/BACKGROUND
Triple-negative invasive ductal carcinoma is a more aggressive type of breast cancer that poses therapeutic challenges. Papillary thyroid carcinoma is generally indolent but has shown aggressive behaviour among Filipinos. As primary carcinomas, both tend to have a good prognosis with early detection and management. However, failure to anticipate a secondary malignancy, when one occurs after the other, can turn a treatable journey into a devastating outcome.

CASE
A 45-year-old female presented with a movable left breast lump 3 years ago. Biopsy confirmed invasive ductal carcinoma with a negative ER/PR/HER2 on immunohistochemistry. She eventually underwent a modified radical mastectomy of the left breast and staged as 2B (T2N1M0) due to the absence of lympho-vascular space invasion and distant metastasis. She completed eight cycles of adjuvant chemotherapy with Doxorubicin and Cyclophosphamide. Post-chemotherapy surveillance confirmed the absence of metastasis. A 2 × 2 cm thyroid nodule was detected on the left anterior neck two years later during routine follow-up. Ultrasound revealed a lobulated solid hypoechoic wider-than-tall nodule in the superior pole of the left lobe (TI-RADS 5). The patient was clinically and biochemically euthyroid. Ultrasound-guided fine needle biopsy identified the presence of Papillary Thyroid Carcinoma (Bethesda Category VI). As such, the patient underwent a total thyroidectomy. Final histopathologic studies confirmed a classic subtype of Papillary Thyroid Carcinoma (ATA Low Risk) without lymphatic, perineural, extrathyroidal invasion and regional lymph node metastasis. Post-operative high-dose radioactive iodine was administered to eliminate any residual thyroid tissue. She was then maintained on levothyroxine suppression and continuously monitored for tumour recurrence.

CONCLUSION
As better understanding of tumorigenesis has revolutionised cancer screening and management, the metachronous coexistence of breast and thyroid carcinoma highlights the importance of multidisciplinary care and vigilant screening for secondary malignancies. Overexpression of estrogen and progesterone, together with shared environmental and genetic factors in breast cancer, have been shown to promote thyroid tumorigenesis and progression.