IMAGES IN CYTOLOGYSection Editor: Shahla Masood, M.D.

Fine-Needle Aspiration of BreastCarcinoma Metastatic toFollicular Variant of PapillaryThyroid CarcinomaJing Yu, M.D., Ph.D., Raja R. Seethala, M.D., Andrew Walls, M.D., and Guoping Cai, M.D.*

A 50-year-old woman who had a history of breast carci-

noma presented with a 3.5-cm right thyroid nodule with

focal intense radiotracer uptake. She subsequently under-

went ultrasound-guided fine-needle aspiration (FNA) biopsy

of the thyroid nodule. The aspirates are cellular and reveal

two distinct epithelial cell populations in a bloody back-

ground with rare colloid (Fig. C-1). The epithelial cells in

one population are large and have a moderate amount of

metaplastic cytoplasm and eccentrically located nuclei with

nuclear hyperchromasia and small nucleoli, arranged as sin-

gle cells and in loosely cohesive clusters (Figs. C-1 and C-

2). The second population is the follicular cells. They are

relatively small and have abundant delicate cytoplasm and

round nuclei with occasional nuclear grooves and rare intra-

nuclear pseudoinclusions, arranged in clusters with a vague

microfollicle pattern (Figs. C-1 and C-3). The patient under-

went partial thyroidectomy, and the resected specimen con-

firmed the diagnosis of breast carcinoma metastatic to fol-

licular variant of papillary thyroid carcinoma (FVPTC).

Metastasis of one malignant tumor to another unrelated

tumor, so-called ‘‘tumor-to-tumor metastasis,’’ is

extremely uncommon. The most common donors of tu-

mor-to-tumor metastasis include lung carcinoma, breast

carcinoma, and melanoma. Thyroid follicular neoplasm

along with meningioma and renal cell carcinoma are

among the most common recipients for tumor-to-tumor

metastasis.1–8 The diagnostic cytomorphologic feature for

tumor-to-tumor metastasis in thyroid is the presence of

two distinct tumor cell populations. However, precise di-

agnosis may be very difficult, if not impossible, based on

cytomorphologic assessment alone.

Cytologically, the tumor cells of metastatic breast carci-

noma in the present case have prominent plasmacytoid

appearance, which may mimic medullary thyroid carci-

noma (MTC). The characteristic spindle cells and amor-

phous amyloid seen in MTC may be present in variable

amount or even absent.9 The intracytoplasmic lumina, tra-

ditionally considered a feature of breast carcinoma, are

also observed in MTC.10 On the other hand, FVPTC

imposes an even bigger diagnostic challenge in the setting

of tumor-to-tumor metastasis. The cellularity of aspirated

follicular cells is lower due to dilution of second meta-

static tumor cells. The subtle cytomorphologic features

such as nuclear grooves and small intranuclear inclusions

may be overlooked when the metastatic tumor cells

become the focus. Thus, ancillary studies such as immu-

nostains or molecular studies may be required to fully

characterize the two populations of tumor cells. Unfortu-

nately, the aspirate from a thyroid FNA biopsy is often

scant, which may preclude a further work up.

The diagnosis of tumor-to-tumor metastasis by FNA bi-

opsy is difficult, but can be facilitated by increasing

awareness of this rare occurrence and securing adequate

material for ancillary studies. The feasibility of such a di-

agnosis can be enhanced by requiring clinical information,

especially previous history of malignancy.

Department of Pathology, University of Pittsburgh Medical Center,Pittsburgh, Pennsylvania

*Correspondence to: Guoping Cai, M.D., Department of Pathology,UPMC Shadyside Hospital, 5230 Centre Avenue, Suite WG02.1, Pitts-burgh, PA 15232. E-mail: caig2@upmc.edu

Received 4 July 2008; Accepted 23 September 2008DOI 10.1002/dc.20992Published online 3 February 2009 in Wiley InterScience (www.

interscience.wiley.com).

' 2009 WILEY-LISS, INC. Diagnostic Cytopathology, Vol 37, No 9 665

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Figs. C-1–C-3. Fig. C-1. Aspirate smears show two distinct epithelial cell populations: the large cell population of metastatic breast carcinoma andthe small cell population of follicular variant of papillary thyroid carcinoma (Diff-Quik stain 3100, inset 3400). Fig. C-2. The tumor cells of meta-static breast carcinoma are large and have moderate amount of metaplastic cytoplasm with prominent plasmacytoid appearance (Diff-Quik stain3400). Fig. C-3. The tumor cells of follicular variant of papillary thyroid carcinoma are small and have delicate cytoplasm with occasional nucleargrooves and rare intranuclear pseudoinclusions (Papanicolaou stain 31000).

YU ET AL.

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