PMC4359859_01
Contrast-enhanced computed tomography images of the tumor. A 2.8 cm sized tumor was present at the left parotid gland. The tumor was relatively circumscribed and contained a low-density area inside.
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ACiCC was again most strongly suspected by our cytological diagnosis. A CT scan showed a 2.8 cm sized mass in the left parotid gland (Figure 1).
Cytomorphology of mammary analogue secretory carcinoma. Tumor cells were seen in a relatively flat sheet with abundant vascular supply (a). Tubules or rosette-like structures were sometimes seen (arrows, (b)). Tumor cells sometimes piled up with scattered detached cells peripherally (c). The cytoplasm of the tumor cells was slightly eosinophilic and the cell border between the tumor cells was indistinct ((d), (e)). Light-greenish material was sometimes observed at the periphery of the tumor cell cluster (arrow), which is now considered to correspond to material secreted by the tumor cells (f). With Giemsa stain, tumor cells showed slightly eosinophilic cytoplasm and intracytoplasmic granules (arrows) were rarely seen (g). Eosinophilic substance (arrowheads) showing slight metachromacy was seen inside tumor tubules/in the background ((g), (h)). (a) to (f) Papanicolaou stain; (a) and (b) FNA material; (c) to (f) imprint material; (g) and (h) Giemsa stain.
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The cell clusters were mostly thin sheet-like, sometimes with slight accumulation, or were seen in an arborizing pattern with a vascular core (Figure 2(a)). Tubule formation was sometimes seen (Figure 2(b)). The cell adhesion between the tumor cells looked rather loose and they seemed easy to detach (Figure 2(c)). The cell border between the tumor cells was indistinct (Figure 2(d)). Individual tumor cells had slightly eosinophilic and granular cytoplasm (Figures 2(d) and 2(e)). Although it was not recognized as such at the time of cytological diagnosis, retrospective review sometimes revealed a light-greenish material corresponding to material secreted by the tumor cells attached to the cell cluster (Figure 2(f)). Giemsa-stained specimen also showed that tumor cells had slightly eosinophilic and granular cytoplasm (Figure 2(g)). Pinkish material showing slight metachromacy was seen inside tubular structures/in the background (Figures 2(f) and 2(g)).
Macroscopic and histological morphology of mammary analogue secretory carcinoma. The cut section of the tumor was uncircumscribed and whitish, invading into the connective tissue surrounding the parotid gland (a). Microscopically, the tumor grew in a nodular fashion with abundant fibrous septa (b). The tumor formed small ducts or microcysts and often had vacuolated cytoplasm (arrows) (c). Tumor cells were relatively uniform and showed morphology similar to intercalated duct (d). Pinkish/mucin-like substances were sometimes seen inside the tumor tubules (e). Immunohistochemically, tumor cells were diffusely and intensely positive for S-100 (f) and partially/intensely positive for mammaglobin (g). (b) to (e) HE stain; (f) immunohistochemistry for S100; (g) immunohistochemistry for mammaglobin.
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Cut sections of the surgical specimen showed a 3.0 x 2.8 x 2.5-cm sized, uncircumscribed, whitish, elastic hard mass in both lobes of the left parotid gland (Figure 3(a)). Histopathologically, the tumor grew partially with a multinodular appearance but often showed invasive growth with fibrotic/hyalinized stroma (Figure 3(b)). In the tumor nodule, tumor cells formed small tubules or acini sometimes with secretory material inside (Figure 3(c)). Tumor cells were relatively uniform, similar to intercalated duct cells, and often had vacuolated cytoplasm (Figure 3(d)). A small portion of the tumor showed the aggregates of irregularly dilated glands with secretory material inside (Figure 3(e)). Immunohistochemically, tumor cells were intensely positive for S-100 (Figure 3(f)), GCDFP-15, and mammaglobin (Figure 3(g)), while ER, PgR, HER2, and p63 were negative.
The analysis of ETV6-NTRK3 fusion transcript. The results of the electrophoresis (a) and direct sequencing (b) revealed the presence of an ETV6-NTRK3 fusion gene. In (a), the arrow indicates the PCR product of the ETV6-NTRK3 transcript. PCR for 
beta-actin and GAPDH was performed as a quality check of the extracted RNA. NC: negative control. L: ladder (molecular marker). In (b), the arrow indicates the fusion point of the ETV6-NTRK3 transcript.
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This analysis revealed the presence of an ETV6-NTRK3 fusion transcript in this tumor (Figures 4(a) and 4(b)).