Keywords
Adenoid cystic carcinoma - fine-needle aspiration cytology - perineural - salivary
glands
Introduction
Adenoid cystic carcinoma (ACC) is a relatively uncommon tumor, with a reported incidence
of 4.5 cases per million individuals.[1] It most commonly involves the salivary glands.[2] Involvement of lacrimal gland, breasts, uterine cervix, esophagus, lungs, and prostate
is exceedingly rare and infrequently reported.[3]
Owing to nonspecific clinicoradiological features, these tumors masquerade other nonneoplastic
and neoplastic entities. On literature search scattered case reports and case series
of site specific ACCs were found without any large study on the incidence, distribution
and clinicopathological features of ACC at different sites. Keeping in view these
considerations, we retrospectively analyzed cases of ACCs over a period of 4 years
in a tertiary care setting. Our study highlights the clinicopathological features
of ACC with special emphasis on the utility of preoperative diagnostic modalities
such as imaging and fine-needle aspiration cytology (FNAC).
Materials and Methods
The archives of Department of Histopathology were retrospectively reviewed from January
2012 to January 2016. Of the 57,890 cases received, cases of ACC were included in
the study. The medical records and clinical details of these patients including preoperative
FNAC and/or radiological findings on computed tomography (CT)/magnetic resonance imaging
(MRI)/mammography were retrieved. FNAC was performed wherever possible. Repeat aspiration
was performed if the first FNA attempt yielded inadequate material or was inconclusive
for diagnosis. Smears were then air dried and stained with May-Grünwald Giemsa stain.
All the patients underwent curative surgery. The excised specimen was fixed in 10%
neutral buffered formalin and sent for histopathological examination. Diagnosis was
confirmed on hematoxylin and eosin (H and E) stained, formalin-fixed paraffin embedded
sections. These tumors were graded as per recommendations by Szanto et al.[4] Tumors containing only tubular or cribriform growth pattern were categorized as
Grade I tumors, tumors containing cribriform or tubular growth with <30% solid component
as grade II tumors and tumors containing >30% solid component as Grade III tumors.
A detailed immunohistochemical (IHC) panel consisting of cytokeratin (CK) (Biocare
Medical, Clone: AE1/AE3), cluster of differentiation 117 (CD117) 117 (Biocare Medical,
Clone: EP10), thyroid transcription factor-1 (TTF-1) (Biocare Medical, Clone: 8G7G3/1),
estrogen receptor (ER) (Thermo Scientific, Clone: SP1), progesterone receptor (PR)
(Thermo Scientific, Clone: SP2), human epidermal growth factor receptor (HER2/neu)
(BioGenex, Clone EP1045Y), and Ki-67 (Thermo Scientific, Clone: SP6) was applied to
all cases. In brief, sections measuring 3–4 μm thick were cut, deparaffinized with
xylene and brought to water through graded levels of alcohol. Endogenous peroxidase
activity was blocked by treating the slides with hydrogen peroxide for 30 min at room
temperature. Antigen retrieval was done by immersing the slides in citrate buffer
using the pressure cooker method. Then, the slides were incubated overnight with the
primary antibody (rabbit polyclonal) at 4°C in a humidified chamber. The following
day secondary antibody was added. The sections were then incubated with di amino benzidine
for visualization of the peroxidase reaction. After being washed in water, the sections
were counter stained with hematoxylin, dehydrated in alcohol, cleared in xylene, and
mounted. IHC was interpreted in a binary fashion as positive or negative. Ki-67 index
was calculated by counting the total number of Ki-67 positive cells in 100 consecutive
tumor cells.
The FNAC smears, H and E stained sections, and IHC slides of all the cases were reviewed
by two pathologists and correlated with the clinical findings including radiology.
Results
Out of 57,890 cases received in the department over a period of 4 years, we found
only 30 cases of ACC [Table 1]. The mean patient age at the time of surgery was 55.5 years (range 19–64 years).
There were 13 male and 17 female patients with a male:female ratio of 1:1.3. Among
these 30 tumors, 10 (33.4%) were located in the submandibular gland, 7 (23.4%) in
the parotid gland, 6 (20%) in the sublingual gland, 2 (6.7%) in the lung and one each
(3.33%) in nasal cavity, breast, cervix, lip, and skin of face.
Table 1
Site distribution of 30 cases of adenoid cystic
carcinoma
|
Site
|
Number of cases (%)
|
|
Submandibular gland
|
10 (33.4)
|
|
Parotid gland
|
7 (23.4)
|
|
Sublingual gland
|
6 (20)
|
|
Lung
|
2 (6.7)
|
|
Breast
|
1 (3.33)
|
|
Cervix
|
1 (3.33)
|
|
Nasal cavity
|
1 (3.33)
|
|
Lip
|
1 (3.33)
|
|
Cutaneous (face)
|
1 (3.33)
|
|
Total
|
30
|
Clinical presentation of these patients was variable and site dependent. All cases
of ACC in head and neck region (26 cases) presented with complaints of a slow growing
painless mass associated with facial pain in two cases and a single case with recurrent
epistaxis. Apart from head and neck, a 35-year-old female patient presented with bleeding
on and off for 5 months while an elderly female presented with a firm immobile breast
lump for 8 months. Two female patients presented with prolonged cough and shortness
of breath lasting for 1 year.
Preoperative imaging was performed in all 30 cases [Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d, [Figure 1]e, [Figure 1]f. Contrast-enhanced CT (CECT) findings were suggestive of a malignant tumor in 28
cases and depicted the extent of the primary lesion accurately. However, definite
categorization of the malignant tumors could not be established in any of these cases.
A single case of parotid gland ACC was misdiagnosed as a benign salivary gland neoplasm
on CECT [Figure 1]a. Mammography findings in an elderly female with a breast lump were suggestive of
malignancy (BIRADS IV) [Figure 1]f. Metastatic deposits in the lung were reported in one patient with submandibular
ACC and one case of sublingual ACC. However, lymph node metastasis was seen in only
a single patient with sublingual ACC.
Figure 1: Contrast enhanced computed tomography image shows (a) Heterogeneously enhancing
mass lesion involving superficial and deep lobes of right parotid gland, (b) Small
lobulated mass lesion just anterior to the left submandibular gland with areas of
necrosis, (c) Heterogeneously enhancing mass in posterior segment of right upper lobe,
(d) Homogeneous mass involving the nasal septum along with bony erosion of medial
wall of right orbit, (e) Heterogeneously enhancing cervical mass seen obstructing
the endocervical canal, (f) Breast mammography image shows a spiculated mass in upper
outer quadrant of left breast suggestive of BIRADS IV
FNAC was performed in all cases except for the mass in uterine cervix due to inaccessibility
of lesion. Further, CT-guided FNAC was performed for the lung lesions. FNA smears
were moderately cellular with cells arranged in variably sized cohesive clusters and
occasional cup shaped fragments [Figure 2]a. The individual tumor cells were small with scant basophilic cytoplasm and central
round hyperchromatic nucleus. Numerous variable sized, spherical, and pink hyaline
globules were seen both within and outside the cell clusters [Figure 2]b. Accurate diagnosis of ACC was made in 82.7% cases (24/29 cases) on FNAC. In the
remaining, two cases of parotid gland swelling and one case of swelling in the submandibular
region yielded paucicellular smears after repeated attempt and were inconclusive for
a definite opinion. However, aspirate smears from one of the swellings on the floor
of mouth and peripheral lung nodule yielded hemorrhagic smears and was inadequate
for diagnosis. Interestingly, a 55-year-old female presented with a firm, slow growing,
ill-defined swelling on the floor of month for 1 year. Simultaneously, she also complained
of a breast lump in the same duration. FNA smears from the sublingual swelling revealed
features of ACC while aspirate smears from breast lump showed infiltrating ductal
carcinoma, suggestive of synchronous breast and minor salivary gland tumor.
Figure 2: Photomicrograph of May Grünwald Giemsa stained fine needle aspiration smears
show; (a) Moderate cellularity with small basaloid cells arranged in cohesive clusters
and occasional cup shaped fragments (inset) (×200). (b) Tumor cells are embedded within
spherical, pink hyaline globules (inset) (×200). Photomicrograph of H and E stained
sections show; (c) Cribriform arrangement of tumor cells forming pseudocysts filled
with basement membrane like basophilic material (×100). (d) Tubular arrangement of
cells which are round to cuboidal with scant eosinophilic cytoplasm and central hyperchromatic
nucleus (×400)
Surgical resection specimens in all patients showed a mean tumor size of 3.2 cm. H
and E stained sections showed cribriform and tubular arrangement of tumor cells forming
pseudocysts filled with basement membrane-like basophilic material. The individual
tumor cells were round to cuboidal with scant eosinophilic cytoplasm and central hyperchromatic
nucleus [Figure 2]c and [Figure 2]d. As per the grading system, 25 cases belonged to Grade I, 4 cases to Grade II and
one case to grade III. Perineural invasion was seen in seven cases (33.33%). On IHC,
all the cases showed cytoplasmic positivity for CK [Figure 3]a. Membranous and cytoplasmic positivity for CD117 was seen in 24 cases (80%) [Figure 3]b. TTF-1 was positive in two cases of pulmonary ACC only [Figure 3]c. Focal HER2/neu immunopositivity was seen in two cases of parotid gland ACC while
ER and PR expression was not observed in any of the 30 cases. ACC of breast was thereby
categorized as a triple-negative breast cancer. Mean Ki-67 score of the 30 cases studied
was 47.8% [Figure 3]d.
Figure 3: On immunohistochemistry tumor cells were positive for; (a) cytokeratin (immunostain,
×200), (b) cluster of differentiation 117 (immunostain, ×200), (c) thyroid transcription
factor-1 (immunostain, ×200), (d) Ki-67 (immunostain, ×200)
Discussion
Although ACC was first described in 1853, the term was denominated by Spies later
in 1930.[5] The usual peak incidence of ACC is between 50 and 60 years of age with a slight
female preponderance,[6] and our results were in concordance with published literature. ACC comprises 10%
of all salivary gland tumors and most commonly affects the submandibular gland followed
by parotid gland.[7] In the present series, similar results were obtained along with localization at
unusual sites such as lung, palate, breast, cervix, and face.
Among the rare cases, ACC of the breast previously known as cylindroma accounts for
<0.1% of all primary breast cancers.[8] The major histopathological differential diagnosis for ACC includes cribriform carcinoma
of breast. However, the latter shows epithelial cells only without basement membrane-like
material. While ACC is categorized as basal – like subtype of breast carcinoma, cribriform
carcinoma usually expresses ER and PR positivity on IHC staining.[9] Due to scarcity of reported cases and variations in the patterns of this tumor,
no definite guidelines for treatment have been established till date. Borrowing from
literature the outcome of these tumors is favorable vis-à -vis other forms of breast
cancer and ACCs of the salivary glands.[10]
The cell of origin for ACC of cervix is proposed to be the “reserve cells” in the
endocervix where it comprises <1% of all cervical carcinoma.[11],[12] Although the exact pathogenesis remains elusive, the role of human papillomavirus
in ACC has been suggested in the past. On the contrary, pulmonary ACC of lung is an
unusual neoplasm arising from the submucosal glands of the tracheobronchial tree and
accounts for 0.04–0.2% of all primary pulmonary tumors.[13] The large airways are most commonly involved in over 80% of cases.[14] Our study included two cases of pulmonary ACC one of which was located peripherally
and yielded hemorrhagic smears of FNAC. The second case of pulmonary ACC was located
along the main bronchus, and CT-guided FNA smears were diagnostic of ACC. Although
aspirate smears usually yield characteristic features of ACC comprising basaloid cells
arranged in clusters and embedded within hyaline globules, the cytomorphological differential
diagnosis in doubtful cases includes carcinoid tumor, small cell carcinoma, and well-differentiated
adenocarcinoma. The absence of hyaline globules and glandular architecture excludes
the diagnosis of carcinoid tumors while clusters of uniform cells with glandular arrangement
are characteristic of well-differentiated adenocarcinoma. Small cell carcinoma on
the contrary is characterized by nuclear molding and nuclear streaking.[15]
Nasal cavity and skin are other unusual sites for ACC with <70 cases of the latter
described in English literature.[16],[17] Histogenesis of primary cutaneous ACC is still not clear and no universally agreed
predisposing factor is known. Clinical assessment of all of the reported cutaneous
ACCs led to a misdiagnosis of a skin appendageal tumor.
ACC is a clinical masquerader and includes a varied spectrum of lesions in the differential
diagnosis clinically. Pleomorphic adenoma, mucoepidermoid carcinoma, and polymorphous
low-grade adenocarcinoma are usually considered in the setting of salivary gland involvement.
At the unusual locations mentioned earlier, clinical diagnosis of this notorious tumor
remains a diagnostic dilemma.
A rather interesting and unusual case of dual primary malignancies was encountered
in our series. A 55-year-old female was simultaneously diagnosed with ACC of floor
of the mouth and infiltrating ductal carcinoma of the breast. The presence of multiple
primary malignancies in a patient can either be detected at the same time (synchronous),
or one cancer may follow the other after a certain period (metachronous). If the initial
primary is the breast, the percentage of patients expected to develop multiple primaries
is 10%.[18] Dual primary malignancies have been identified with increasing frequency, possibly
due to the increase in life expectancy of cancer survivors and more robust cancer
screening protocols. The causal factors for this occurrence include persistent carcinogen
exposure, ionizing radiation, and the increasing use of hormonal therapies, genetic
manipulation, and immunomodulators.[19] However, the exact causal relationship of the dual malignancies in our patient could
not be ascertained. This particular case is the first case of dual primary malignancy,
i.e., ACC of floor of mouth and infiltrating ductal carcinoma of breast in a single
patient, thereby highlighting that presence of a lesion anatomically away from the
primary malignancy should be labeled as a metastatic focus only after detailed evaluation
including histopathological confirmation.
Preoperative diagnosis of ACC is a challenging task for the radiologists due to nonspecific
signs. CT scan helps in localization of the lesions and delineates the extent of malignancy.
In our study, CT scan identified malignant masses in all cases but was unable to categorize
the lesion in any. On the other hand, FNAC is a simple, minimally invasive, and cost-effective
first line outpatient department investigation which can render a preoperative diagnosis
of ACC. However, intraoral lesions pose a diagnostic difficulty owing to the inaccessibility
and technical difficulty in performing mucosal FNAC and often yield hemorrhagic/inadequate
aspirates as seen in two of our cases. Thus, the diagnosis of ACC is solely based
on morphology. However, morphology alone cannot differentiate primary from metastatic
ACCs and a complete clinicoradiological work up is mandatory to rule out any focus
of primary tumor elsewhere.
The expression of IHC markers has been evaluated as potential prognostic indicators
in ACC. Proliferation marker Ki-67 comes across as a promising immunostain showing
an increased expression with increasing amounts of solid (grade III) component and
a definite correlation with worse prognosis.[20],[21] CD117 (c-KIT) immunoreactivity has also been evaluated in a variety of tumors due
to the presence of targeted inhibitor therapy against it. KIT positivity has been
commonly observed in gastrointestinal stromal tumors and seminoma, rare cases of synovial
sarcoma and Ewing sarcoma, as well as melanocytic tumors like nevi and malignant melanomas.
However, its expression in carcinomas is rather rare, with the exception of small
cell lung carcinoma and ACC.[22] In our series, positivity for CD117 was seen in 80% of cases. Since our study was
a retrospective analysis, inability to analyse c-KIT mutation and response to inhibitor
therapy was a drawback. Similar to CD117, targeted therapy against HER2/neu makes
it a valuable marker. However, low prevalence of HER2/neu overexpression in ACC as
also seen in our study limits the clinical utility of Herceptin therapy.[23]
Another immunostain studied was TTF-1. Expression of this marker is observed in both
normal and neoplastic lung and thyroid tissues. Similar to publisher data, only two
cases of pulmonary ACC showed positivity for this marker in contrast to other sites.
Therefore, TTF-1 is considered as a reliable marker of pulmonary and in the setting
of metastasis. Recently, Jungsuk et al. concluded that TTF-1 expression should be
interpreted in the context of the clinical setting, radiologic findings as it can
be expressed in ACCs metastatic to the lung despite being negative in the primary
tumor site.[24]
ACC exhibits a paradoxical clinical behavior. Initially, the tumor presents as a slow-growing
indolent mass, but the subsequent course is progressive and usually associated with
multiple recurrences. Hematogenous spread to distant organs such as lung and bone
is well documented with regional nodal involvement being rather rare.[25] Of the 30 cases studied, we found only one patient with lung and regional nodal
metastasis each. Fewer cases with distant metastatic foci were observed which may
be attributed to a shorter follow-up in.
While tumor stage using the American Joint Committee on Cancer is considered as the
most reliable prognostic indicator,[26] some authors have emphasized the importance of histologic subtyping with tubular
subtype carrying the best prognosis in contrast to solid subtype. Although the prognostic
significance of this grading system has been questioned time and again,[27] the presence of a solid component has been a consistent predictor of poor prognosis
in several series.[28] Moreover, there is a strong correlation between site of origin and prognosis. ACC
involving the major salivary glands has a more favorable outcome in comparison to
minor salivary glands. Localization of ACC in the nasal cavity and paranasal sinuses
carries the worse prognosis than in any other area of the head and neck region.[29]
Furthermore, the paradoxical behavior of ACC is highlighted by an optimistically high
5-year survival rate in contrast to a dismally low 10–20 year survival rate.[30]
Till date, surgery and radiotherapy still remain the main course of treatment. Nonetheless,
after resection of the primary tumor, this notorious tumor is associated with local
and distant recurrences. This high-recurrence rate likely reflects the known tendency
for perineural invasion. Careful documentation of perineural invasion during staging
is especially important as it stands as an independent prognostic factor.[18] Various authors have reported duration of recurrence varying from 18 months to 67
months thereby making long-term follow in these patients mandatory. Periodic radiological
assessment especially MRI may identify changes indicative of recurrent disease many
months before clinical evidence.[10]
To conclude, ACC is a malignant tumor with a deceptively benign histologic appearance
characterized by indolent, locally invasive growth with high propensity for local
recurrence and distant metastasis. Chest examination should invariably be done, as
these tumors may have propensity for pulmonary metastasis. Trials of targeted therapy
to date have not yet identified an agent with sufficient activity to be deemed standard
in the treatment of advanced ACC. The immediate future of research in this field of
the molecular pathogenesis of ACC will not only be of diagnostic importance but will
also derive targeted therapies for this neoplasm.
