Background
Low-grade cribriform cystadenocarcinoma (LGCCC) is a rare neoplasm of salivary gland. Originally, it was described as a variant of salivary duct carcinoma (SDC) by Delgado et al. in 1996 [
1]. LGCCC usually occurs in elder people with a female predominance of 2:1. Parotid gland is the most common site of involvement [
1‐
6]. Presentation in the palate [
7], submandibular gland [
2], intraparotid lymph node [
2,
6] and accessory parotid gland [
8] may occur but rare. LGCCC is characterized by the papillary-cystic or cribriform proliferation pattern and resembles the low-grade ductal carcinoma in situ or atypical ductal hyperplasia of the breast in histology and biological features. LGCCC was originally denominated as low-grade salivary duct carcinoma (LGSDC) in order to distinguish with the conventional SDC. In contrast with the LGCCC, conventional SDC exhibits highly aggressive malignancy and high-grade histology similar to an invasive ductal carcinoma of the breast. However, no definite association was found between LGCCC and conventional SDC; therefore, the third WHO classification regards this neoplasm as a variant of cystadenocarcinoma due to its cystic morphology [
9].
Histologically, LGCCC was composed of single or multiple cystically enlarged ducts accompanied by adjacent intraductal proliferation. Various structures, such as cystic structures, loose cribriform and micropapillae pattern or solid area, could be observed in LGCCC. The typical cyst structures are lined by small or multilayered mild ductal cells with finely dispersed chromatin and small nucleoli. These tumor cells are diffusely strong positive for S100. Myoepithelial markers highlight the tumor cells rimming the cystic spaces, confirming the intraductal nature of LGCCC. Based on the histological features, LGCCC should be distinguished with other common parotid tumors including papillocystic variant of acinic cell carcinoma (PCV-ACC), conventional SDC, cystadenocarcinoma, polymorphous low-grade adenocarcinoma (PLGA), carcinoma ex pleomorphic adenoma and mammary analogue secretory carcinoma (MASC).
Discussion
Like other rare tumors in parotid glands, LGCCC is a low-grade malignant tumor with indolent clinical behavior [
10‐
12]. In the third WHO classification, it is listed under a separate heading although regarding as a variant of cystadenocarcinoma [
9]. To date, there are nine papers totally reported 35 cases of LGCCC. The reported cases and the two cases in this paper were summarized in Table
1. In these patients, the majority of LGCCC occurred in older patients (median 62 years) without obvious gender preponderance (Male: Female=15:21; one case with gender unavailable) though the third WHO classification described that the tumor had a female predominance. Among the cases listed in Table
1, thirty-five tumors arose from parotid glands both in the superficial and deep lobes, including three cases occurred in the intraparotid lymph node and one occurred in accessory parotid gland. The remaining two tumors arose in the palate and submandibular gland. Therefore, all the LGCCCs reported by now occurred in large salivary glands except one controversial report on hard palate. The tumor size varied from 0.9 to 4 cm. Among the cases with follow-up available, no one had recurrence or died because of the tumor. According the clinically indolent behavior, most of the cases were treated with parotidectomy without radiotherapy.
Table 1
Reported cases of the low-grade cribriform cystadenocarcinoma in the English-Language Literature and their prognosis
1 | Delgado et al. 1996 | 58 | M | Parotid (superficial lobe) | 1 cm | Superficial parotidectomy | not mentioned |
2 | | 62 | F | Parotid | 0.7 cm | Parotidectomy | not mentioned |
3 | | 32 | F | Right parotid (superficial lobe) | 1.1 cm | Parotidectomy, radiotherapy | NED, 144 mos |
4 | | 63 | M | Right parotid (superficial lobe) | 1.3 cm | Parotidectomy | NED, 132 mos |
5 | | 74 | M | Left parotid | 1.8 cm | Parotidectomy | NED, 72 mos |
6 | | 56 | F | Right parotid | 1 cm | Parotidectomy | NED, 24 mos |
7 | | 42 | M | Left parotid (superficial lobe) | 1.2 cm | Parotidectomy | NED, 24 mos |
8 | | 69 | F | Right parotid (intraparotid lymph node) | 4 cm | Parotidectomy | NED, 24 mos |
9 | | 69 | M | Left parotid | 0.9 cm | Parotidectomy | - |
10 | | 52 | F | Right parotid (deep lobe) | 0.8 cm | Parotidectomy, radiotherapy | NED, 9 mos |
11 | Tatemoto et al. 1996 | 58 | F | Palate | 1 cm | Not mentioned | NED, 30 mos |
12 | Brandwein-Gensler et al. 2004 | 62 | F 8 cases M 7 cases U 1 case | Parotid 15 cases (including one case from intraparotid lymph node) | Not mentioned | Not mentioned | NED, 12 mos |
13 | | 82 | NED, 44 mos |
14 | | 78 | NED, 17 mos |
15 | | 72 | NED, 108 mos |
16 | | 93 | NED, 24 mos |
17 | | | NED, 30 mos |
18 | | | NED, 62 mos |
19 | | 64 | Submandibular gland 1 case | NED, 33 mos |
20 | | 66 | Not mentioned |
21 | | 57 | NED, 30 mos |
22 | | 63 | Not mentioned |
23 | | 64 | NED, 6 mos |
24 | | 62 | NED, 132 mos |
25 | | 72 | NED, 40 mos |
26 | | 76 | NED, 24 mos |
27 | | 54 | Not mentioned |
28 | Weinreb et al. 2006 | 50 | F | Right parotid | 2 cm | Superficial parotidectomy | NED, 5 mos |
29 | | 73 | M | Left parotid | 1.8 cm | Superficial parotidectomy and supraomohyoid neck dissection | NED, 60 mos |
30 | | 67 | F | Right parotid | 2.5 cm | Right total parotidectomy and chemotherapy and radiation therapy | Not mentioned |
31 | Arai et al. 2009 | 32 | F | Right parotid | 2.8 cm | Right partial parotidectomy | NED, 24 mos |
32 | Laco et al. 2010 | 50 | F | Right parotideomasseteric area | 1.5 cm | Enucleation of the tumor | NED, 24 mos |
33 | Nakatsuka et al. 2011 | 27 | M | Accessory parotid gland | 1.5 cm | Local excision of the tumor | NED, 3 mos |
34 | | 56 | F | Left parotid | 3 cm | Parotidectomy | NED, 12 mos |
35 | Weinreb et al. 2011 | 59 | F | Left parotid (intraparotid lymph node) | 3.5 cm | Not mentioned | Not mentioned |
36 | Current case | 48 | M | Left parotid | 2cm | Parotidectomy | NED, 16 mos |
37 | Current case | 59 | F | Right parotid | 3.5 cm | Parotidectomy | NED, 7 mos |
Grossly, the clinical suggestion of LGCCC is used to be Warthin tumor according to the morphologic feature, that is, a slowly growing cystic mass. Histologically, the tumor is unencapsulated and composed of single or multiple cysts with an intraductal proliferation. The cystic cavity is in line with cytologically bland ductal cells. The intraductal proliferation has a cribriform pattern with “sieve-like spaces” similar to breast proliferations. The majority of the tumor is intraductal; however, small areas of invasion may be present. A total of 7/37 (19%) cases summarized in Table
1 have focal stromal invasion. The tumor cells usually display little cytologic atypia and low mitotic rate [
9]. Sometimes, the tumor cells have PAS-positive/diastase-resistant microvacuoles and yellow-brown, lipofuscin-like pigment. There is often associated hemorrhage, cholesterol clefts and hemosiderin-laden macrophages due to cyst rupture, while vascular and/or perineural invasion and comedonecrosis is absent in this tumor.
Immunohistochemically, LGCCC is characterized by diffusely strong positive for S100. However, Weinreb
et al. [
13] and Arai
et al. [
3] reported two cases of LGCCC with rarely negative for S100. All tumors examined for Her-2/neu oncoprotein, including our case, were negative. Most of the tumor structures have continuous myoepithelial rim confirmed by detection of myoepithelial markers, such as, CK5/6, CK14, SMA, and p63, thus clarifying an in situ nature of the neoplasm. Typically, admixture of luminal and myoepithelial cells is absent.
The differential diagnosis of LGCCC includes PCV-ACC, conventional SDC, cystadenocarcinoma, PLGA, carcinoma ex pleomorphic adenoma and MASC. PCV-ACC resembles LGCCC according to the intracytoplasmic PAS-positive/diastase-resistant granules (zymogen) and hemosiderin [
14]. In contrast to LGCCC, the more common microcystic growth pattern in PCV-ACC is usually seen adjacent to cystopapillary areas and display granular basophilic cytoplasm. PCV-ACC does not exhibit predominance of the intraductal component in histology and the intracytoplasmic vacuoles are uniform in size. Compared with LGCCC, PCV-ACC is predominantly negative (about 90%) for S100 and focally expressed if present [
9]. In addition, PCV-ACC mainly occurs in young people, while LGCCC usually affects older people.
Conventional SDC is a high-grade adenocarcinoma that is common in elder people over 50 years of age [
9]. Histologically, SDC resembles a high-grade invasive ductal carcinoma of the breast, frequently accompanied by comedo necrosis and cribriform proliferation [
9]. SDC exhibits an apocrine-like appearance with positivity for GCDFP-15 and androgen receptor, which is occasionally observed in LGCCC, but SDC is negative for S-100. In addition, SDC usually exhibits a high Ki-67 labeling index. Occasional cases of SDC in situ (SDCIS) have been described [
15‐
17]. The in situ–like appearance or noninvasive cribriform growth pattern make it hard to distinguish between SDCIS and LGCCC. In contrast to LGCCC, the atypical cells in SDCIS exhibit high nuclear pleomorphism and AR-positive/S100-negative profile. Weinreb
et al. [
6] reported a series of 3 intraductal neoplasms interpreted as LGCCC with some nuclear atypia of the tumor cells, all expressing AR and in 2 cases also showing S100 expression. Thus, they consider their LGCCC cases to be a low-grade variant of SDC with a potential for transformation into a high-grade carcinoma. At present, the relationship between LGCCC and SDCIS remains unclear although the current WHO classification considering LGCCC as a variant of cystadenocarcinoma. LGCCC may be either a separate entity based on distinctive immunohistochemical profile or an extremely low-grade end of the spectrum of SDCIS.
Recently, a new entity in the salivary gland called MASC has been described [
18,
19], which shows a similar microvacuolar appearance to LGCCC and may have any of solid, cystic and papillary architectures. Similar to LGCCC, MASC is also positive for S100. All these characteristics make it difficult to distinguish between LGCCC and MASC. Although no cases of MASC with an intraductal growth pattern have been described, it should be noted that only one IDC/LGCCC was included in the control group tested for the ETV6-NTRK3 fusion in Skalova et al’s original description of MASC. For now, the presence of a complete myoepithelial layer around tumor nests is considered specific to LGCCC instead of MASC.
In the current WHO classification, LGCCC is regard as a variant of cystadenocarcinoma according to the histological features. However, conventional cystadenocarcinoma tends to be an invasive tumor and lacks the overall resemblance to intraductal breast proliferation. PLGA and carcinoma ex pleomorphic adenoma should also be considered when rendering a diagnosis of LGCCC. PLGA can be distinguished from LGCCC by its distinctive neurotropism and infiltrative lobular, trabecular, and tubular patterns. The transition from myoepithelium to stromal spindle cell and myxoid or cartilaginous stroma is the typical features of carcinoma ex pleomorphic adenoma, which is not observed in LGCCC.
Both of the cases exhibited the typical features of LGCCC, that is, intraductal proliferation and bland ductal cells arranged in a cribriform pattern whichresembled the low-grade breast lesions. Most of the tumor nests or cribriform structures in these two cases were rimming by the continuous myoepithelialium which confirmed by p63, thus, clarify an in situ nature of the neoplasm. The tumor cells in both cases were diffusely strong positive for S100. In addition, the Ki67 index in our cases was under 5%. All these findings supported the diagnosis of LGCCC, although the dilated cystic structures were not observed in Case 2.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
LW analyzed the data and wrote the manuscript as a major contributor. YL, XL and DZ helped to perform the immunochemical staining. QL, XQ and EW helped to revise the discussion section of this manuscript. All authors have read and approved the final manuscript.