DNA flow cytometry of acinic cell carcinomas of major salivary glands

Correlation of Histopathological Variants, Cellular DNA Content, and Clinical Outcome in Adenoid Cystic Carcinoma of the Salivary Glands

OBJECTIVE: To study the correlation between flow cytometrically measured DNA ploidy with prognostically important histopathologic groups and clinical outcome in patients with adenoid cystic carcinoma of the salivary glands.

STUDY DESIGN: 46 tumor specimens were analyzed flow cytometrically for DNA content and assessed for histological grade. Correlations were made between tumor DNA ploidy and histopathological grade, and disease-free and overall survival of these patients.

RESULTS: Of the 46 patients, 31 had a cribiform/tubular histologic pattern, and 15 had a solid pattern. 84% of the tumors with cribriform/tubular pattern were DNA diploid, compared with 33% of tumors that were graded solid. This difference proved to be statistically significant (χ 2 11.75, P = 0.0006). Overall and disease-free survival periods were longer for patients with DNA diploid tumors in both groups, 63% vs. 36% and 62% vs 38%, respectively.

CONCLUSIONS: Tumor DNA ploidy correlates with prognostically important tumor histopathology as well as overall and disease-free survival in patients with adenoid cystic carcinoma of the salivary gland. EBM rating: B-3.

Salivary acinic cell carcinoma: reappraisal and update

Epidemiologic and clinicopathologic features, therapeutic strategies, and prognosis for acinic cell carcinoma of the major and minor salivary glands are critically reviewed. We explore histopathologic, histochemical, electron microscopic and immunohistochemical aspects and discuss histologic grading, histogenesis, animal models, and genetic events. In the context of possible diagnostic difficulties, the relationship to mammary analog secretory carcinoma is probed and a classification is suggested. Areas of controversy or uncertainty, which may benefit from further investigations, are also highlighted.

"Dedifferentiation" and high-grade transformation in salivary gland carcinomas

"Dedifferentiation" and/or high-grade transformation (HGT) has been described in a variety of salivary gland carcinomas, including acinic cell carcinoma, adenoid cystic carcinoma, epithelial-myoepithelial carcinoma, polymorphous low-grade adenocarcinoma, myoepithelial carcinoma, low-grade mucoepidermoid carcinoma and hyalinizing clear cell carcinoma, although the phenomenon is a rare event. Recent authors tend to preferably use the term HGT instead of "dedifferentiation" in these cases. HGT-tumors are composed of conventional carcinomas juxtaposed with areas of HG morphology, usually either poorly differentiated adenocarcinoma or "undifferentiated" carcinoma, in which the original line of differentiation is no longer evident. The HG component is generally composed of solid nests, sometimes occurring in cribriform pattern of anaplastic cells with large vesicular pleomorphic nuclei, prominent nucleoli and abundant cytoplasm. Frequent mitoses and extensive necrosis is evident. The Ki-67 labeling index is consistently higher in the HG component. p53 abnormalities have been demonstrated in the transformed component in a few examples, but the frequency varies by the histologic type. HER-2/neu overexpression and/or gene amplification is considerably exceptional. The molecular-genetic mechanisms responsible for the pathway of HGT in salivary gland carcinomas largely still remain to be elucidated. Salivary gland carcinomas with HGT have been shown to be more aggressive than conventional carcinomas with a poorer prognosis, accompanied by higher local recurrence rate and propensity for cervical lymph node metastasis, suggesting the need for wider resection and neck dissection.

Common Malignant Salivary Gland Epithelial Tumors

Malignant salivary gland epithelial tumors are histologically diverse with at least 24 recognized distinct entities. In general, malignant tumors account for 15% to 30% of parotid tumors, 40% to 45% of submandibular tumors, 70% to 90% of sublingual tumors, and 50% of minor salivary tumors. Common malignancies include mucoepidermoid carcinoma, adenoid cystic carcinoma, acinic cell carcinoma, salivary duct carcinoma, carcinoma ex pleomorphic adenoma, polymorphous lowgrade adenocarcinoma, and myoepithelial carcinoma. Each tumor type has its own unique histologic variants and prognostic pathologic features, and only mucoepidermoid carcinomas have a formalized grading system. The molecular pathogenesis of certain tumors, such as mucoepidermoid carcinoma and adenoid cystic carcinoma, has recently begun to be elucidated.

Current concepts on dedifferentiation/high-grade transformation in salivary gland tumors

The concept of dedifferentiation had previously been used in salivary gland carcinomas. Recently, the term “high-grade transformation” was introduced for adenoid cystic carcinoma, acinic cell carcinoma, epithelial-myoepithelial carcinoma, and polymorphous low-grade adenocarcinoma and may better reflect this phenomenon, although transformation into moderately differentiated adenocarcinoma (i.e., not “high grade”) has also been described. Among the immunohistochemical markers, Ki-67 seems to be the only one that can help distinguish between the conventional and transformed components; however, the combination of morphological criteria is still sovereign. The overexpression of p53 was observed in the transformed component in all tumor types studied, despite few cases having been demonstrated to carry mutations or deletions in TP53 gene. Genetic studies in salivary gland tumors with dedifferentiation/high-grade transformation are rare and deserve further investigation. This paper aims at providing an overview on the recent concepts in histopathological classification of salivary gland tumors, complemented by immunohistochemical and genetic findings.

DNA ploidy analysis in salivary gland tumours by image cytometry

AIM

To determine whether DNA ploidy by image cytometry is a good diagnostic tool to distinguish benign and malignant salivary gland tumours.

METHODS

A total of 62 salivary gland tumours were studied. Cases were histologically diagnosed [haematoxylin and eosin (H&E)]. According to the World Health Organization (WHO) classification, there were 14 mucoepidermoid carcinomas (MEC), 11 adenoid cystic carcinomas (ACC), 10 pleomorphic adenomas (PA), 10 carcinoma ex PA (CEPA), 9 acinic cell carcinomas (ACCa), 3 polymorphous low-grade adenocarcinomas (PLGA), 2 papillary cystadenocarcinomas (PC), 1 myoepithelial carcinoma (MC), 1 undifferentiated carcinoma (UC) and 1 mucinous adenocarcinoma (MA). Paraffin sections (40 microm) were micro-dissected to isolate tumour areas; cell nuclei were extracted and Feulgen-stained cytospin monolayers were analysed using a DNA image cytometry system. For each case, DNA index (DI) was calculated relative to internal controls (lymphocytes; DI=1.0). Cases were categorized as diploid or aneuploid and the proportion of cells over 5c was also calculated.

RESULTS

Fifty-three of 62 salivary gland tumours were uniformly diploid. Only nine cases were aneuploid: five CEPA, one low-grade MEC, one PC, one UC and one MA.

CONCLUSIONS

The vast majority of salivary gland tumours were diploid. High-grade malignancies may be aneuploid, and ploidy may be useful to identify malignant change in atypical PA. Further, larger studies are needed to confirm our results and to further evaluate the usefulness of the technique in high-grade lesions.

Dedifferentiation occurring in adenoid cystic carcinoma of the tongue

A 61-year-old man came to the University of Granada School of Dentistry complaining of a mass involving his ventral tongue. Histopathologic examination of the excised specimen showed adenoid cystic carcinoma in which cribriform and tubular patterns were observed, juxtaposed with an undifferentiated carcinoma, large-cell type. No cervical lymph node metastasis was present, and the patient is alive and free of disease 5 years after treatment. To our knowledge, no similar cases have been reported thus far, though other salivary gland malignancies have been described in association with undifferentiated carcinoma, especially in the parotid gland. These neoplasms have been highly aggressive, and the adequacy of the primary surgical resection may be critical in determining the ultimate prognosis and survival.

Cytogenetic and molecular genetic demonstration of polyclonality in an acinic cell carcinoma

The paradigm that human malignancies are monoclonal has been questioned during recent years by the finding of unrelated, cytogenetically aberrant clones in short-term cultures from certain tumour types, notably carcinomas of the breast, skin and upper aerodigestive tract. In order to analyse whether cytogenetically unrelated clones are also unrelated at the molecular level, we analysed the X-chromosome inactivation status in cell cultures from a cytogenetically highly polyclonal acinic cell carcinoma of the parotid gland. By using cell cultures dominated by a single abnormal clone, obtained through in vitro culturing for 3-5 passages, we showed that the different clones must indeed have originated from different cells.

Genetic alterations in acinic cell carcinoma of the parotid gland determined by microsatellite analysis

We investigated, for the first time, the genetic alterations at certain chromosomal loci in 25 primary parotid acinic cell carcinomas to define the most frequently altered chromosomal regions and their association with pathologic features and DNA content analysis. Our results showed that 21 (84.0%) of the tumors had alteration in at least one of the loci tested. In general, chromosomal regions at chromosomes 4p, 5q, 6p, and 17p were more frequently altered than those on chromosomes 1p and 1q, 4q, 5p, and 6q. Certain markers at 4p15-16, 6p25-qter, and 17p11 regions showed the highest incidence of LOH, suggesting the presence of tumor suppressor genes associated with the oncogenesis of these tumors. LOH was significantly associated only with tumor grade. No apparent correlation between LOH and other clinicopathologic and DNA content characteristics was identified. Our study broadly defined the chromosomal arms and loci that may be targeted for further localization of the minimally deleted regions involved in the tumorigenesis of these tumors.

Fine-needle sample of salivary gland lesions. V: Cytology of 22 cases of acinic cell carcinoma with histologic correlation

Fine-needle sampling (FNS) of 22 acinic cell carcinomas, including 17 primary tumors, 4 local recurrences, and 1 lymph node metastasis was performed preoperatively in 17 patients. Cytologic diagnoses were concordant with histology in 3 (13.7%) cases, whereas 15 (68.2%) cases were cytologically classified as malignant, 2 (9.1%) as suspicious, and 1 (4.5%) as benign (pleomorphic adenoma). The material was unsatisfactory for cytologic evaluation in 1 (4.5%) case. Preoperative FNS technique is, therefore, useful in acinic cell carcinoma with a concordant malignant/suspicious rate of 91%.

Polymorphous low-grade adenocarcinoma: flow cytometric, p53, and PCNA analysis

Polymorphous low-grade adenocarcinoma of minor salivary glands (terminal duct carcinoma, lobular carcinoma) was first defined more than a decade ago. A 17% recurrence rate and a 9% metastasis rate have been reported. Fifteen formalin-fixed, paraffin-embedded archival cases were analyzed. Ploidy and proliferative activity were evaluated with flow cytometric analysis. Demonstration of an abnormal p53 gene product and proliferative cell nuclear antigen analyses were also performed with routine immunohistochemical procedures. The purpose of this investigation was to evaluate these parameters and determine if a correlation existed. Flow cytometry was performed on 10 cases; 3 showed an aneuploid cell line (mean, S-phase diploid tumor cells 5.9%; S-phase aneuploid 26.7%). Products of a mutation of the p53 tumor suppressor gene have been noted to accumulate in salivary gland tumors, both benign and malignant. Qualitative assessment revealed p53 positive staining in 4 of 15 tumors; positive cells comprised 5% to 10% of the tumor. The percentage of tumor cells positive for proliferative cell nuclear antigen staining ranged from 0.5% to 70%. There was no correlation between proliferative activity as determined by proliferative cell nuclear antigen when compared with results of flow cytometric analysis except for one case that exhibited p53 staining, a 26% proliferative cell nuclear antigen fraction, and a distinct aneuploid cell line.

Dedifferentiated acinic cell carcinoma of the parotid gland: a distinct rarely described entity

A case of dedifferentiated acinic cell carcinoma of the parotid gland is presented. A 46-year-old man presented with a parotid gland mass. At surgery the tumor was found adherent to the temporal bone and cervical adenopathy was present. Treatment included radical parotidectomy and intraoperative radiotherapy. Histologically, the tumor was a composite of a usual low-grade acinic cell carcinoma and high-grade, poorly differentiated carcinoma. Cervical lymph node metastases were composed entirely of high-grade carcinoma. Immunohistochemically, both low- and high-grade malignant components were negative for p53 oncoprotein expression. Moreover, polymerase chain reaction and nonisotopic single-stranded conformational polymorphism analyses were consistent with a germ line configuration of the p53 gene, exons five through eight, in both low- and high-grade elements of the tumor. The literature on this unusual variant of acinic cell carcinoma is reviewed.

Well-differentiated acinic cell carcinoma of salivary glands associated with lymphoid stroma

In a multicenter study, 69 acinic cell carcinomas of the salivary glands were identified, of which 12 constituted what the authors believe to be a distinct subgroup. Their most noticeable feature was a dense lymphoid stroma with well-developed germinal centers, surrounding a sometimes scanty epithelial component, which in each case had a microcystic growth pattern. All these tumors were enveloped by a thin fibrous pseudocapsule, thus mimicking an intraparotid lymph node containing a metastasis. All 12 cases showed low MIB1 proliferative activity, with a mean index of 1.7% (range, 0.5 to 3.7). All patients remained well without recurrence or metastasis in followup periods of 19 months to 14 years. A second subgroup of nine acinic cell carcinomas also possessed a heavy lymphoid stroma with germinal centers, but its distribution was more patchy than in the first subgroup, and in addition, the fibrous pseudo-capsule was incomplete or absent. In each case the epithelial growth pattern was other than microcystic. These tumors had significantly higher MIB1 indices (mean, 17%; range, 3.4 to 45). In contrast to the first subgroup, only three of nine patients remained well with no further disease. The other six patients developed recurrences or metastases, and two died of disseminated cancer. In view of the clinical and pathological data, it is speculated that the tumor foci lacking lymphoid stroma in each of the second subgroup possibly represented a clone of high-grade malignancy arising within a low-grade acinic cell carcinoma with lymphoid stroma.

Parotid acinic cell carcinoma with undifferentiated spindle cell transformation

This report describes a 59-year-old black man who had an acinic cell carcinoma with associated malignant spindle cell transformation in the parotid gland. To the best of our knowledge, a similar lesion in the salivary gland has not been previously reported.

DNA flow cytometry of reclassified subtypes of malignant salivary gland tumors

Malignant salivary gland tumors are rare, constitute a heterogeneous group and are often difficult to diagnose histologically. This is borne out by the fact that in the present study 43.2% of 118 salivary gland tumors originally diagnosed as mucoepidermoid, acinic cell and adenoid cystic carcinomas had their original diagnosis altered upon reclassification. Patients with confirmed adenoid cystic carcinomas had a much worse prognosis than those with mucoepidermoid and acinic cell carcinomas. DNA flow cytometry showed that very few of the above mentioned three types of malignant neoplasms revealed aneuploid DNA stemlines, indicating that this is not a relevant prognostic tumor marker within the groups. However, several of the tumors that had their diagnosis changed, mostly to undifferentiated adeno- or squamous cell carcinomas, showed aneuploid DNA stemlines. The survival time of patients with aneuploid tumors was considerably reduced compared to those with diploid tumors. Among confirmed acinic cell, mucoepidermoid and adenoid cystic carcinomas the S-phase fraction was a significant prognostic factor, as it was among all tumors examined. This indicates that DNA aneuploidy and S-phase fractions are potential prognostic factors for malignant salivary gland tumors, and that DNA flow cytometry may assist the characterization of such tumors.

Cell proliferation correlates with prognosis in acinic cell carcinomas of salivary gland origin. Immunohistochemical study of 30 cases using the MIB 1 antibody in formalin-fixed paraffin sections

Immunohistochemical staining with the MIB 1 antibody was used to assess cell proliferation in 30 cases of acinic cell carcinoma of salivary glands. Until now, no prognostic factors have been available for these rare tumours. The MIB 1 monoclonal antibody recognizes the Ki-67 antigen in formalin-fixed, paraffin-embedded tissues. A MIB 1 index was developed as a means of expressing the percentage of MIB 1-positive tumour cell nuclei, and the tumours were scored without prior information of clinical behaviour. The staining results were then compared with the clinical outcome of the patients. All eight patients who developed tumour recurrences had MIB 1 indices higher than 5 per cent. Tumour recurrences could be predicted even in cases of bland morphology and low mitotic rate. Three patients died of their recurrent tumours, and had MIB 1 indices of 56.2, 12.7, 7.8 per cent in their primary tumours. Five of seven patients with MIB 1 indices higher than 10 per cent had unfavourable outcomes. None of the 17 patients with MIB 1 indices lower than 5 per cent developed recurrences during follow-up periods up to 30 years. The present results indicate that MIB 1 staining appears to be a significant prognostic factor in acinic cell carcinomas of salivary gland origin.

Heterogeneity of salivary gland tumors studied by flow cytometry

Intratumor DNA heterogeneity was investigated by flow cytometric analysis of multiple samples taken from different sites of 8 benign and 16 malignant primarily resected salivary gland tumors. All benign tumors had diploid DNA content. The overall incidence of DNA diploidy in 16 malignant cases examined was 50%. Intratumor differences in DNA ploidy were observed in four malignant tumors (25%); 2 of these 4 heterogeneous tumors contained both aneuploid and diploid cell clones. The remaining 12 tumors showed a homogeneous DNA content in the different specimens; 8 were diploid, 3 aneuploid, and 1 was polypoid. The DNA nondiploid tumors were clinically more advanced than the DNA diploid ones (p < 0.01). The tumor proliferation rate (fraction of cells in S-phase) was higher in DNA nondiploid samples than in diploid ones (p < 0.01). The DNA nondiploid tumors seemed to recur more often than DNA diploid ones did. The data emphasize the usefulness of DNA measurements for the characterization of malignant salivary gland tumors but also the importance of adequate sampling in assessing their DNA ploidy.

Salivary neoplasms of the palate: a flow cytometric and clinicopathological analysis

In order to test the clinical and prognostic significance of flow cytometrically assessed DNA content in minor salivary gland tumours we evaluated 75 neoplasms of the palate, 55 of which were carcinomas. Benign neoplasms were exclusively DNA diploid with low S-phase fractions while 22 per cent of malignant tumours manifested a DNA aneuploidy and 23.5 per cent high S-phase fractions (> 5 per cent). Significant statistical correlations between DNA content and tumour size, histological grade, lymph node metastasis and lethality were observed. Our findings suggest a potentially important role for flow-cytometry in the evaluation of these neoplasms.