Keywords
Acinic cell carcinoma - cutaneous metastasis - salivary gland neoplasms
Introduction
Acinic cell carcinoma (ACC) is a low-grade malignant neoplasm of the salivary gland
that constitutes approximately 17% of all primary salivary gland malignancies, parotid
gland being the most common site (80%).[1]
[2] It affects a large population in the second to seventh decade of life, with a slight
female preponderance. Despite being a low grade and slow growing malignancy, a recurrence
rate of 35% is reported. Distant metastasis of 16% has been reported, often many years
after the initial presentation. We report, here, a case of widespread cutaneous and
subcutaneous metastatic ACC of the parotid gland, occurring 20 years after the primary
resection.
Case Report
A 50-year-old male presented with two rapidly enlarging tender nodules on the scalp
and distal finger of the hand. On physical examination, they were crusted erythematous
nodules with focal areas of alopecia on the scalp. Multiple other cutaneous and subcutaneous
nodules were evident on the right and left hand and left foot and calf. [Figure 1], [2], [3], [4] show the cutaneous nodules on scalp, both hands, and left foot and calf on further
examination of the patient. Core biopsies of the scalp and hand nodules were sent
for histopathological examination (HPE). Hematoxylin and eosin (H and E) stained sections
showed tumor cells arranged in a lobular, microcystic, and acinar pattern. [Figure 5] and [6] show the low power and high power view (×10 and ×40, respectively), of round to
polygonal tumor cells with basophilic granular to clear cytoplasm, and hyperchromatic
nucleus and an inconspicuous to single nucleoli. Acini were comprised of cuboidal
cells with clear to vacuolated cytoplasm showing PAS-positive cytoplasmic granules
and pleomorphic, hyperchromatic nuclei with frequent atypical mitosis. A diagnosis
of low-grade metastatic carcinoma was offered. The primary sites under consideration
were the salivary gland, kidney, GIT, and the thyroid gland. Immunohistochemistry
(IHC) revealed positive staining for AE1/AE3 [Figure 7], CK7, and DOG1 [Figure 8] and were negative for CK20, vimentin [Figure 9], p63, CDX2, CEA, TTF, PAX8, and S100. PAX8-negative immunostaining ruled out thyroid
and renal origin of the metastatic tumor. CK7 positivity and CK20 negativity favored
salivary gland origin. p63-negative staining ruled out myoepithelial salivary gland
tumor. Further, DOG1 membranous and cytoplasmic positivity and P63 negativity favored
ACC. The patient was reexamined clinically after the pathological diagnosis, and a
preauricular scar was noted on the patient’s face, confirming a prior parotid surgery
20 years back. Thus, with a history of a previous surgery in the parotid region, HPE
and IHC, a diagnosis of metastatic ACC was offered.
Figure 1: Cutaneous nodule on the scalp
Figure 2: Nodules on both hands
Figure 3: Cutaneous nodule on foot
Figure 4: Cutaneous nodule on the calf
Figure 5: Low power (×10) view of hematoxylin- and eosin-stained section of round
to polygonal tumor cells with basophilic granular cytoplasm with hyperchromatic nucleus
and inconspicuous single nucleoli
Figure 6: 40X view of Haematoxylin & Eosin stained section showing nests of tumor
cells beneath the epidermis of skin
Figure 7: AE1 positivity
Figure 8: DOG1 positivity
Figure 9: Vimentin negativity
Discussion
ACC is an uncommon salivary gland tumor. Among the salivary glands, parotid gland
is most commonly affected. A single case report with widespread cutaneous metastasis
has been reported.[3] In spite of being a low-grade malignant tumor, ACC has a propensity for late recurrence
and metastasis, often many years after initial presentation. Most common sites of
metastasis are the lungs, brain, and lymph nodes.[4] Case reports of isolated concurrent cutaneous involvement have been reported.[5]
[6] Miki et al. have suggested a minimum 10-year follow-up for patients with ACC in view of its
propensity for late recurrences.[7] According to the World Health Organization classification, ACC is a malignant epithelial
neoplasm of the salivary gland in which, at least some of the neoplastic cells demonstrate
serous acinar cell differentiation, characterized by cytoplasmic zymogen secretory
granules. Histomorphologically, ACC can display various growth patterns such as solid,
microcystic, papillary, cystic, follicular, or various combinations of the above.
Tumor cells in ACC usually resemble the serous acinar cells which are round to polygonal.
The cytoplasm is fine or coarsely granular or may be clear. Cytoplasmic zymogen granules
are the key to diagnosis which are positive to special stains such as PAS. Nucleus
is eccentric with inconspicuous nucleoli. IHC shows focal positive or negative CK7
staining. Recent studies show that DOG1 is a promising marker in the diagnosis of
ACC. DOG1 positivity and p63 negativity show 93%–100% sensitivity in the diagnosis
of ACC.[8]
[9]
Conclusion
Possibility of metastasis from ACC should be considered in differential diagnosis
of new cutaneous nodules in a patient with a history of salivary gland neoplasm. Combination
of HPE and IHC can lead to the confirmation of the diagnosis. Although it is a low-grade
and slow-growing tumor, it can present with disseminated cutaneous metastasis, even
after decades of the primary presentation. Hence, it requires very long-term follow-ups
as early diagnosis can lead to prompt investigations and early interventions.
Declaration of patient consent
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In the form the patient(s) has/have given his/her/their consent for his/her/their
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understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
