Pathologic Doppelgänger: Thyroid-like intrahepatic cholangiocarcinoma with synchronous primary thyroid carcinoma in a young woman.

Intrahepatic cholangiocarcinoma (ICC) accounts for 8-10% of all malignant liver tumors. Preponderance for elderly males and occurrence of varied morphological patterns in ICC is well known. Recent reports have described a newly recognized variant of thyroid-like cholangiocarcinoma. Herein, we present a hitherto unreported synchronous occurrence of an intrahepatic thyroid-like cholangiocarcinoma and a separate thyroid carcinoma in a 23-year-old post-partum woman. Both tumors displayed striking resemblance to follicular variant of papillary thyroid carcinoma (FVPTC) however exhibited disparate immunohistochemical profiles: the intrahepatic tumor was positive for CK7 and CK19, and negative for TTF-1, PAX-8 and thyroglobulin whereas, the thyroid tumor was positive for TTF-1, thyroglobulin and PAX-8. Young age, female proclivity, large mass at presentation and unique histology in thyroid-like ICC hint towards a distinctive subset of ICC. Awareness and recognition of this rare entity is essential, not only for accurate diagnosis, but also for gathering information on its biology and clinical behavior. Synchronous occurrence with a FVPTC is a challenging scenario that can simulate metastatic disease and mislead subsequent patient management. Whether morphologic similarity points to an underlying linkage between the two different tumors needs exploration.