Discussion:
The world health organization (WHO) has defined AdCC as ”a basaloid
tumor containing epithelial and myoepithelial cells in diverse
morphological configurations, such as tubular, cribriform, and solid
patterns. Its clinical course is relentless and usually has a fatal
outcome”(9).
A review of literature was carried out in this study, which is
demonstrated in table 1.
Eleven cases of AdCC in the buccal mucosa have been reported via
articles thus far. In this article, two other cases of AdCC in the
buccal mucosa have been reported. The first case was a 39-year-old
female with a painless exophytic mass in the buccal mucosa for more than
two months. The second case was a 37-year-old male with a mass in the
left buccal mucosa which had been existent for 8 months.
In Vidyalakshmi et al’s case, the swelling had arisen after a left upper
posterior tooth was extracted. Furthermore, a single submandibular lymph
node on the left side of the patient’s face was palpable, a phenomenon
rarely occurring in adenoid cystic carcinoma. The lymph node was firm,
mobile, non-tender, and had a size of less than 1 cm(14).
The patient in Dalirsani et al’s study had a leukoedema accompanying the
AdCC lesion on the same side. Superficial ulceration was evident in the
aforementioned tumoral lesion, unlike the reported cases in this
article, which were free of ulcers. At the time, a stage I diagnosis
(T2N0M0) was made, and
the patient underwent 35 cycles of radiotherapy and chemotherapy. Two
years later, the patient was once again referred to the department, with
a chief complaint of a 1.5 cm firm mass on his right frontal region.
Following an incisional biopsy, a diagnosis of Adenoid Cystic Carcinoma
was established, and the patient was referred for chemotherapy and
further investigations to an oncologist. Following a CT-scan, a stage IV
lung metastasis was diagnosed. The patient underwent 3 cycles of
cisplatin and 5-fluorouracil chemotherapy, which were ineffective in
reducing the tumor’s size. Therefore, 3 more cycles were carried out
with Taxol and carboplatin. The patient remained under oncologists’
supervision until date(16).
In the case reported by Bansal et al, the patient who had received
treatment for adenoid cystic carcinoma of the buccal mucosa in 2005, was
referred again, with a chief complaint of coughs for 4 months,
breathlessness for the last 2 months, and fever for 20 days. A CECT scan
view of thorax and upper abdomen identified parenchymal metastatic
deposits. Multiple osseous metastatic deposits and a few small
mediastinal lymph nodes were observed. Fine needle aspiration cytology
(FNAC) confirmed that the metastatic deposits belonged to the Adenoid
Cystic Carcinoma, of which the patient was diagnosed with in 2005. The
patient was referred to the department of oncology for further
management(8).
In Kumar et al’s study (2018), Brain MRI and Chest X-ray revealed no
evidence of distant metastases(17).
There are three histopathological views for adenoid cystic carcinoma:
the cribriform, tubular, and solid patterns. The cribriform pattern,
being the most common, has a view of islands of basaloid cells,
surrounded by cyst-like spaces in different sizes, forming a ”Swiss
cheese” pattern. The tubular histologic subtype has a closely similar
display, but with cells arranged and organized in nests surrounded by
different amounts of often hyalinized eosinophilic stroma. The solid
subtype manifests aggregates of basaloid cells without tubular or
pseudocystic formations(3).Since polymorphism is a common phenomenon in
AdCC, it’s possible to see all three aforementioned patterns in one
specimen. Therefore, MD Anderson introduced a pathological grading
system, to which is now contributed worldwide(19):
Grade I: tubular and cribriform together, without a solid pattern.
Grade II: mostly cribriform, with less than 30% of solid pattern.
Grade III: solid being the predominant subtype.
The differential diagnosis includes polymorphous low grade
adenocarcinoma (PLGA), salivary duct carcinoma, and basaloid squamous
cell carcinoma(18). PLGA demonstrates large tumoral cells than AdCC with
vesicular nuclei versus small basaloid cells of AdCC. Single file
appearance can also help to distinguish PLGA from AdCC. Salivary duct
carcinoma (SDC) does not show cribriform pattern of AdCC and PLGA. On
the other hand, SDC is a high grade carcinoma with prominent nuclear
pleomorphism and atypical mitotic figures. Comedo-type necrosis can help
to diagnosis between SDC and other tumors of salivary glands(20).
Basaloid squamous cell carcinoma (BSCC) is a high grade malignancy of
keratinocytes which can mimic AdCC, histopatologically. Superficially
squamous cell carcinoma, large eosinophilic cytoplasm of tumoral cells
and keratin pearls can help to distinguish between BSCC and AdCC.
Ancillary studies such as immunohistochemistry examinations can help to
definitive diagnosis.
Perineural invasion, sometimes associating Adenoid Cystic Carcinoma, is
defined as ”a form of direct primary spread of neoplasm which may not
necessarily be macroscopically continuous with the main focus of the
tumor, but is usually microscopically continuous”. The second and third
branches of the trigeminal nerve are most frequently affected. The
descending branches of the facial nerve and smaller cranial branches can
also get involved. Perineural involvement is claimed to be an indicator
of poor prognosis(19). Furthermore, it can increase the chances of
recurrence. Recent data argues that intraneural invasion, rather than
perineural, can have a higher impact on the survival rate in the AdCC of
the head and neck(3).
In Naik et al’s case, slight perineural thickening of the facial nerve
was observed. In a more precise examination, perineural and intraneural
invasion were evident, due to which the patient had mild degrees of
facial palsy(13).
Contrary to other types of carcinomas, distant hematogenous metastases
are much more common than regional lymph node metastases in AdCC.
Hematogenous metastases in AdCC can remain asymptomatic for a
considerable period of time, especially lung metastases, which
apparently has a slow progress rate(19).
Singh et al (2010) used paraclinical assessments, such as
ultrasonography of upper abdomen, non-contrast proton MRI of the oral
cavity, PA view of the chest, axial CT scan of the head and face,
lateral neck radiograph, submentovertex view of the skull (35°), PA view
of the pelvic girdle, and CT scan of chest, to rule out metastasis(10).
The primary goal of treatment for patients affected with AdCC is local
control of the tumor, normal function, and preventing distant
metastases(21). Radical surgery with wide resection margins may not be
sufficient per se, as achieving disease-free margins can be difficult
due to AdCC’s propensity to perineural invasion and some lesions’
challenging anatomical access(2). Radiation is noncompulsory for small
tumors (T1N0) but must be considered for
cases having low-grade tumors in association with perineural invasion,
or evidence of tumor seeding during surgery. A lower radiation dose has
also been recommended for patients with tumors located in lymphatically
rich areas (22). Using radiotherapy as primary treatment is proposed
when surgery is not feasible(3). In addition, radiation can be a
standard treatment for alleviating bone and brain metastases(23).
As AdCC’s sensitivity to chemotherapy is relatively low, systemic
chemotherapy for AdCC remains controversial. On the other hand,
chemotherapeutic treatment has proven to be effective in a rather low
percentage of patients with recurrences or metastases. The first-line
chemotherapy choice is highly dependent on patients’ comorbidities and
characteristics(2).
Tumors of the minor salivary glands can more easily infiltrate the
surrounding extra-glandular tissues, increasing dissemination of the
tumor cells and thus rendering resection with disease-free margins more
difficult. The cribriform variant is believed to have the best prognosis
while the solid pattern has the worst, with the tubular subtype having
an intermediate-level prognosis(19).