We extracted 3 cases of salivary gland HC from a pathology file and one of the author’s consultation files (K.K.) for the period from 1992–2019. All cases involved primary salivary gland HC. All of the slides for these cases were reevaluated, with particular attention paid to the two different histological components, the presence or absence of transitional zones, and the absence of primary neoplasms from other organs, especially in the head and neck region.
The patient was an 85-year-old Japanese male, who had noticed a rapidly swelling mass in the left parotid region some years ago. He was admitted to his local clinic and was diagnosed with adenocarcinoma after a fine-needle aspiration biopsy (FNAB). He was admitted to our hospital 20 months later. An immovable mass was present in the left parotid region, but the patient was not suffering any pain or facial nerve paralysis. Magnetic resonance imaging (MRI) showed an ill-defined high intensity region and a focal low intensity region on T1-weighted imaging, and a low intensity region and focal high intensity region on T2-weighted imaging (Figure 1A). Positron emission tomography (PET) showed accumulation in the left parotid gland mass. Under a clinical diagnosis of left parotid gland cancer (pT4aN0M0), total parotidectomy with skin and facial nerve resection was performed. No postoperative treatment was administered. There was no evidence of local recurrence or metastasis at 2 years after the operation.
Macroscopically, an ill-defined yellowish-white mass, with partial cystic changes, and yellowish-green contents inside the cystic spaces, was seen (Figure 1B). The tumor measured 4.0 x 3.2 x 5.3 cm.
Histologically, the tumor was composed of a combination of an SDC and an SqCC. The major component (i.e., the SDC), which accounted for 80% of the tumor, had a classical and typical histology, involving microcystic to marked cystic dilation, and exhibited Roman-bridge structures and comedonecrosis by cancer cells (Figure 1C), together with eosinophilic cytoplasm, marked nuclear pleomorphism, and a high mitotic rate. Immunohistochemical staining was performed on 4-μm-thick sections, which were cut from formalin-fixed and paraffin-embedded tissue. The tumors were considered to be diffusely positive (+++), positive (++), partially positive (+), and focally positive (F+) when ≥50%, 20–49%, 10–19%, and 1–9% of the neoplastic cells were positive, respectively. The HER2 score was estimated according to the criteria of Wolff et al . Epidermal growth factor receptor (EGFR) expression was categorized as positive or negative. According to Boyle’s evaluation criteria , a tumor was considered to be p53-positive if >50% of the tumor cell nuclei showed strong reactivity, which was considered to be indicative of a p53 point mutation. Carcinoma cells that exhibited no p53 immunostaining despite weak positivity being seen in the infiltrating lymphocytes raised a high suspicion of the deletion (i.e., loss) of p53. Weak of sparse p53 immunostaining was considered to be indicative of the presence of wild-type p53. The antibodies used in this study and the results of the immunohistochemical analysis are summarized in Table 2. Immunostaining showed that the SDC component was strongly positive for cytokeratin (CK) 7, gross cystic disease fluid protein (GCDFP)-15, and androgen receptor (AR), and partially positive for EGFR and CK5/6 (Figures 1D), but negative for human epidermal growth factor receptor 2 (HER2), p63, and p40. Therefore, the SDC was subclassified into the apocrine B phenotype, according to Takase’s classification of SDC .
At least 20% of the tumor was made up of nest-like structures composed of proliferating cancer cells, which exhibited keratinization and squamous differentiation (Figure 1E). The cancer cells in this component displayed marked nuclear atypia, single cell keratinization, and intercellular bridges. This component was considered to be a moderately differentiated SqCC. Immunostaining indicated that this component was diffusely positive for CK5/6 (Figure 1F), p63, p40, and EGFR, and focally positive for CK7, but entirely negative for GCDFP-15, AR, and HER2, which are SDC markers.
As both components were focally and weakly positive for p53, they were considered to exhibit the wild-type pattern. The Ki-67 indices of the SDC and SqCC components were 58% and 43%, respectively. Both components were well demarcated, but some areas showed mixed nests composed of both SDC and SqCC.
We finally diagnosed the patient with HC composed of SDC and SqCC.
The patient was a 79-year-old Japanese female, who suffered from swelling of the left parotid region and a disturbance of oral opening. She noticed a small painless mass in the left parotid region. The mass rapidly enlarged, and she was admitted to another hospital a month later. An immovable mass was seen in the left parotid region, but no lymph node swelling or facial nerve paralysis was observed. FNAB and MRI showed no malignancy at that time. After approximately 3 months, FNAB was performed again, and the lesion was cytologically diagnosed as SqCC. Computed tomography (CT) revealed an ill-defined irregularly shaped mass in the left parotid gland, and MRI showed a region of iso-intensity on T1-weighted imaging and low intensity on T2-weighted imaging. PET only showed accumulation in the left parotid mass and did not show any other primary lesion. Under a clinical diagnosis of left parotid gland cancer (cT4aN0M0), left total parotidectomy and left mandibulectomy were performed. Postoperative radiotherapy (66 Gy) was administered. There was no evidence of recurrence or metastasis at 7 months after the operation.
Macroscopically, a single mass was seen (Figure 2A). An examination of the cut surface of the tumor revealed an ill-defined, yellowish-white mass. The central portion of the mass was somewhat whitish.
Histologically, the major component, which accounted for approximately 65% of the tumor, was an SqCC. This component showed marked keratinization, squamous differentiation, and intercellular bridges (Figure 2B). Immunostaining indicated that the cancer cells were diffusely positive for CK5/6, p63, and p40 (Supplemental figure 2) and partially positive for CK8, but negative for neural cell adhesion molecule (NCAM), chromogranin-A, synaptophysin, insulinoma-associated protein (INSM)1, and CK20.
On the other hand, the central portion of the mass was composed of sheet-like and/or nest-like structures, containing large atypical polygonal cells, with relatively loose connections among the tumor cells (Figure 2C). They infrequently displayed rosette-like structures, but the central necrosis was frequently seen. Immunostaining indicated that they were positive for NCAM and CK8, and partially positive for synaptophysin and INSM1 (Figure 2D). Only a few cells were positive for chromogranin-A. On the other hand, the tumor cells were entirely negative for CK5/6, p63, and p40, which are squamous cell markers. Therefore, this component was considered to be an LCNEC.
The Ki-67 labeling indices of the SqCC and LCNEC were 51% and 68%, respectively. The border between the two components was irregular, but the components could be clearly divided via immunostaining (Figure 2E). No obviously transitional zone was observed. As the SqCC component was strongly positive for p53 and the LCNEC component was weakly positive for p53, the SqCC displayed a mutation pattern, and the LCNEC exhibited the wild type pattern (Figure 2F and 2G).
We finally diagnosed the patient with HC composed of SqCC and LCNEC.
The patient was a 66-year-old Japanese male, who had developed a swollen mass on the right side of his neck. As the mass enlarged rapidly and was painful when pressure was applied to it, the patient was admitted to a local clinic, and a FNAB resulted in a diagnosis of a “malignant tumor, suspected, especially, SDC”. The patient was admitted to our hospital one month later. An immovable mass was present in the right parotid region, and the patient was experiencing pain and facial nerve paralysis. Under a clinical diagnosis of right parotid gland cancer (pT4aN2bM0), total parotidectomy with skin and facial nerve resection was performed. Postoperative chemoradiotherapy was administered, but the patient stopped attending follow-up examinations after 2 years.
Macroscopically, an ill-defined yellowish-white mass, which exhibited partial lobulated growth and slight cystic changes, was seen (Figure 3A). The tumor measured approximately 3.3 x 3.0 x 4.8 cm.
Histologically, the tumor was composed of a combination of an SDC and an EMC. The EMC component, which accounted for 55% of the tumor, exhibited the typical histology; i.e., it demonstrated a bi-phasic growth pattern, involving inner ductal cells and outer clear cells (Figure 3B). These cells displayed mild to moderate cellular atypia, and a low mitotic rate, and apocrine differentiation of the inner ductal cells, e.g., eosinophilic cytoplasm and sprouting on the luminal side, was also observed. Immunostaining showed that the inner cells of this component were positive for EMA and CK7 (Figure 3C) and partially positive for CK5/6, whereas the outer clear cells were positive for CK14, CK5/6, alpha-smooth muscle actin (α-SMA), p63, p40, vimentin, and Wilms’ tumor (WT)-1 (Figure 3D). The inner cells were also positive for EGFR, but they were negative for HER2. Therefore, this component was considered to be an EMC.
Approximately 45% of the tumor was composed of proliferating atypical ductal cells, which exhibited marked cellular atypia and eosinophilic cytoplasm. The tumor cells displayed the cystic-papillary, Roman bridge, and solid nest patterns, as well as partial comedonecrosis (Figure 3E). The mitotic rate was relatively high. Immunostaining indicated that they were positive for EMA, CK7, AR, GCDFP-15, and HER2 (2+) (Figures 3F and G), but negative for EGFR and myoepithelial markers. Therefore, this component was considered to be an SDC.
A transitional zone between the SDC and EMC was observed. Atypical apocrine cells were present among the clear myoepithelial cells of the EMC component (Figure 4). As both components were focally positive for p53, they were considered to display the wild-type pattern. The Ki-67 labeling indices of the SDC and EMC components were 23% and 18%, respectively (Supplemental figure 12A and 1B). Therefore, according to Takase’s classification , the SDC component belonged to apocrine A subtype.
We finally diagnosed the patient with HC composed of EMC and SDC.