biostudies-literatureUnknown10(6)Rizwan A<h4>Background/objective</h4>Medullary thyroid carcinoma (MTC) is an uncommon thyroid cancer (TC), rarely found in hyperfunctioning goiter.<h4>Case report</h4>We present a case of a woman treated for breast carcinoma (BCA) found to have a benign hyperfunctioning nodular goiter, its likely transformation to MTC, and its treatment. Family history revealed papillary thyroid cancer in her nephew.<h4>Discussion</h4>Most TCs in hyperfunctioning nodules are differentiated carcinomas. Familial MTC or MTC in association with multiple endocrine neoplasia 2 is the expected genetic association in this case.<h4>Conclusion</h4>The association of BCA and MTC may have been coincidental, given the high prevalence of BCA in females. It could have been the result of a common genetic precursor of both tumors AACE clinical case reports249-252https://www.ebi.ac.uk/biostudies/studies/S-EPMC11680752biostudies-literatureMedullary Thyroid Carcinoma in the Background of Non-neoplastic Toxic Nodular Goiter.PMC11680752Ameen AAkhter SSaad MRizwan AFatima SfalseMedullary Thyroid Carcinoma in the Background of Non-neoplastic Toxic Nodular Goiter.<h4>Background/objective</h4>Medullary thyroid carcinoma (MTC) is an uncommon thyroid cancer (TC), rarely found in hyperfunctioning goiter.<h4>Case report</h4>We present a case of a woman treated for breast carcinoma (BCA) found to have a benign hyperfunctioning nodular goiter, its likely transformation to MTC, and its treatment. Family history revealed papillary thyroid cancer in her nephew.<h4>Discussion</h4>Most TCs in hyperfunctioning nodules are differentiated carcinomas. Familial MTC or MTC in association with multiple endocrine neoplasia 2 is the expected genetic association in this case.<h4>Conclusion</h4>The association of BCA and MTC may have been coincidental, given the high prevalence of BCA in females. It could have been the result of a common genetic precursor of both tumors 2024-01-01T00:00:00Z2024 Nov-Dec2025-04-04T02:36:41.816Z2025-04-04T02:36:41.816ZS-EPMC116807523973449910.1016/j.aace.2024.08.008