Submucosal Gland/Duct Adenoma

Adenomas that develop from the submucosal glands are rare. They are usually histologically similar to those that arise from the minor salivary glands. This is not surprising because, embryologically, the esophageal submucosal glands are considered a continuation of the minor salivary glands of the oropharynx. They are usually submucosal and develop as well-circumscribed lesions that resemble pleomorphic adenomas⁹ or, more rarely, pancreatic or ovary-like serous cystadenomas.¹⁰

Microscopically, adenomas that develop from the submucosal gland ducts show a mixture of tubal, cystic, and papillary growth patterns similar to intraductal papillomas of the breast or sialadenoma papilliferum of the salivary glands.¹¹ The epithelium typically contains two cell layers (similar to the normal submucosal gland ducts) with only mild to moderate cytologic atypia and infrequent mitoses (Fig. 24.3, A). Other adenomas may resemble salivary gland Warthin tumors (see Fig. 24.3, B). The immunophenotype of the tumor cells is also similar to that of the normal esophageal gland ducts.¹² A mixed inflammatory infiltrate may be present as well. Most of these tumors behave in a benign fashion,¹³ although rare carcinomas have been reported.¹⁴

Polypoid Dysplasia in Barrett’s Esophagus

Adenoma-like polypoid dysplastic lesions may develop in BE (see Chapter 14). Endoscopically, these lesions usually appear as well-defined sessile or pedunculated polyps that range in size from 0.5 to 1.5 cm and usually occur in the middle or distal esophagus within areas of BE (Fig. 24.4). Histologically, these polyps are composed of a tubular or tubulovillous proliferation of low- or high-grade dysplastic epithelium, similar in appearance to colonic adenomas. The polyp epithelium is usually of the intestinal type, similar to the surrounding BE, but it may also show a gastric (foveolar) phenotype or mixed features of both.¹⁵

In one study, these lesions showed proliferative and molecular abnormalities (loss of heterozygosity of APC and TP53) similar to those of flat dysplasia and probably should be treated in a similar fashion.¹⁶ In fact, of the 10 cases reported, 9 were associated with adenocarcinoma, illustrating their high malignant potential.¹⁶ Because of the high association with flat dysplasia in the nonpolypoid Barrett’s mucosa, treatment by polypectomy is not considered adequate. Affected patients should be treated according to standard protocols for flat Barrett’s dysplasia, taking into account the extent, location, and grade of dysplasia in the esophagus as a whole.

Heterotopias

Gastric, thyroid, parathyroid, pancreatic, or even sebaceous tissue may be present as heterotopias in the esophagus. These deposits are presumed to be congenital in origin, although, as discussed later, some possible relationships with clinical conditions such as GERD and BE have been proposed.

Gastric heterotopia (“inlet patch”) is by far the most common type, being present in an estimated 2% to 11% of the general population.^27–29 These lesions are usually located in the upper third of the esophagus. Although they are often asymptomatic, they may give rise to symptoms that result from complications of acid secretion, such as heartburn, dysphagia, active esophagitis, ulceration, bleeding, stricture, and perforation. Patients with Helicobacter pylori gastritis frequently show concurrent colonization of the heterotopic mucosa.³⁰ The diagnosis is established by finding gastric glandular and surface epithelium (usually with parietal cells) in the esophagus in patients without intervening BE (Fig. 24.6, A). Some investigators have found a positive correlation with the presence of BE, although the basis for this association, if any, is unknown.^27,29 Rarely, adenocarcinoma may develop in gastric heterotopia (see Fig. 24.6, B),^31,32 and an intraductal papillary mucinous neoplasm arising from a pancreatic heterotopia has been reported.³³

Heterotopic sebaceous glands are the second most common form of heterotopia in the esophagus. They may occur at any level of the esophagus, are frequently multiple, and usually appear as slightly elevated, yellowish lesions, 1 to 2 mm in diameter.³⁴ Microscopically, these lesions show sebaceous cells within the epithelium or in the lamina propria (Fig. 24.7). Sebaceous cells are microvesicular and contain vacuolated cytoplasm filled with lipid substances. An excretory duct, with or without a connection to the surface epithelium, may be present as well. One study suggested that sebaceous glands may represent a metaplastic process because of their frequent association with reflux esophagitis and expression of cytokeratin 14 (CK14), which has been demonstrated in cell lines to represent the progeny of dormant stem cells.³⁵

Pseudoepitheliomatous Hyperplasia

Pseudoepitheliomatous hyperplasia is a morphologic pattern of reactive squamous epithelium that most commonly occurs adjacent to healing ulcers. It is characterized by parallel, elongated, and typically evenly spaced and uniform columns (pegs) of highly reactive squamous cells with prominent nucleoli and mitoses, which may extend deep into the lamina propria (Fig. 24.8). Inflammation, both acute and chronic, is usually present, and this assists in recognizing the reactive nature of the cell proliferation. Lack of surface maturation (nucleated cells at surface) and parakeratosis may be present as well. Its appearance may simulate invasive squamous cell carcinoma, although the lack of either cytologic atypia or deeply infiltrative growth supports its benign nature.³⁶ Furthermore, the squamous cells in reactive hyperplasia usually retain their polarity with respect to each other (absence of overlapping nuclei) and with respect to the basement membrane. Nevertheless, if the columns (pegs) of squamous epithelium are irregular and nonuniform, particularly in areas immediately adjacent to ulcers, and this feature is present in abundance, suspicion for a malignant process should be higher.

On occasion, this pseudoepitheliomatous reaction may be endoscopically visible and polypoid; some authors refer to these lesions as “hyperplastic” or “inflammatory” polyps.³⁷ In addition, polypoid foci of pseudoepitheliomatous hyperplasia may be confused with the endophytic type of squamous papilloma. However, the latter lesions usually lack the significant inflammation and epithelial damage associated with hyperplasia.

Dysplastic epithelium appears erythematous, friable, and irregular in more than 80% of cases.⁵⁰ Erosions, plaques, and nodules may also be present. However, dysplasia may appear completely normal endoscopically. Mucosal staining with Lugol iodine may be helpful to highlight dysplastic mucosa and has been advocated as a means of improving the sensitivity of endoscopic biopsy surveillance in high-risk populations.⁵³ When available, enhanced endoscopic visualization techniques such as narrow-band imaging are also helpful in highlighting dysplastic mucosa that is otherwise grossly nondescript.⁵⁴ Dysplastic cells may also be harvested by exfoliative balloon cytology, a technique that is often used for screening in high-risk areas such as China (see Chapter 3).⁵⁵

Microscopic Pathology

Dysplastic squamous epithelium is characterized by a combination of architectural and cytologic abnormalities that vary in extent and severity, and this is reflected in the grade (Fig. 24.9). The epithelium is usually hypertrophic but may be atrophic in rare circumstances. Dysplasia may involve the basal layer only or the full thickness of the epithelium. In 20% of cases, dysplastic epithelium spreads into esophageal mucosal gland ducts and simulates stromal invasion.⁵⁶ Low-grade dysplasia reveals involvement of the basal third to half of the squamous epithelium with neoplastic cells, whereas high-grade lesions show complete or almost complete involvement of the native squamous epithelium. Dysplastic cells may occasionally grow as isolated cells in a horizontal pagetoid fashion, although this pattern must be distinguished from pagetoid involvement of the squamous epithelium by adenocarcinoma.^57,58

Cytologic changes include nuclear hyperchromasia, pleomorphism, increased nucleus-to-cytoplasm (N : C) ratio, and increased mitotic rate. The chromatin of dysplastic cells is usually coarse and may be associated with thickening of the nuclear membrane. Nucleoli may be present but are not a consistent feature and are not specific because they are also frequently present in reactive squamous epithelium (discussed later). When present, nucleoli may be unusually large in size and irregular in shape. Architecturally, dysplastic cells display disorganization, loss of polarity, overlapping nuclei, and lack of surface maturation, which are key features in helping to distinguish true dysplasia from non-neoplastic (reactive) processes (see Fig. 24.9, C). Mitotic figures are usually increased in number and may be found at any level of the epithelium (base, midepithelium, or surface). Abnormal (tripolar or disorganized) mitotic figures may be present as well, particularly in high-grade lesions.

Rarely, precursor dysplastic lesions may reveal a proliferation of disorganized large cells (with a normal or even low N : C ratio) with open irregular nuclei, prominent enlarged and irregular single or multiple nucleoli, peripheral condensation of chromatin, and multinucleation (see Fig. 24.9, D and E). In these cases, the border between the epithelium and the lamina propria is often highly irregular, showing sharp, budding, or bulbous expansions of epithelium protruding deep into the lamina propria. This type of dysplastic epithelium is often associated with inflammation and surface maturation, although the latter to a much lesser degree than in either normal or reactive squamous epithelium. In these cases, distinguishing dysplastic epithelium from either markedly reactive squamous epithelium or very well-differentiated squamous cell carcinoma may be extremely difficult. Often, repeat biopsies from deeper portions of the lesion and close correlation with the gross endoscopic appearance are necessary to help establish a final diagnosis. In these cases, invasion should not be diagnosed unless there is unequivocal evidence of irregular clusters of neoplastic cells within the deep lamina propria that are clearly disconnected from the overlying surface epithelium (on deeper levels of tissue sectioning) and associated with a peritumoral stromal desmoplastic response.

Differential Diagnosis (Reactive versus Neoplastic)

Squamous dysplasia must be distinguished from reactive epithelial changes associated with esophagitis. Although regenerating squamous cells may show mild nuclear enlargement, hyperchromasia, and expansion of the basal cell layers, they lack significant nuclear pleomorphism, overlapping nuclei, and nuclear crowding and do not display abnormal mitoses (see Fig. 24.9). Unlike in dysplasia, the chromatin is typically fine and homogeneous, and nucleoli, when present, are small and regular in shape. Architecturally, reactive squamous epithelium often displays some degree of surface maturation. Essential to the benign, non-neoplastic diagnosis is the fact that the basal and suprabasal layers maintain their polarity and orderly spacing in reactive lesions. Mucosal inflammation frequently accompanies reactive squamous epithelium, and in the presence of inflammation, a diagnosis of dysplasia should be rendered with caution. In biopsy specimens in which the epithelial changes appear sufficiently marked to suggest dysplasia but a reactive process cannot be excluded because of inflammation, a diagnosis of “indefinite for dysplasia” is appropriate. In such cases, follow-up biopsies after treatment of the underlying esophagitis frequently help resolve the diagnostic uncertainty. The results of ancillary stains, such as strong nuclear staining for TP53 (indicative of inactivating mutations) and extensive, suprabasal cell proliferation highlighted by the proliferation marker Ki67, may also support a diagnosis of dysplasia in problematic cases.⁴⁹ Histologic features useful in the differential diagnosis of squamous dysplasia are summarized in Table 24.2.

In biopsy specimens from patients who have received chemotherapy or radiotherapy, the squamous epithelium may contain markedly atypical cells with enlarged hyperchromatic nuclei that raise the possibility of dysplasia. However, in contrast to dysplasia, these cells do not have an increased N : C ratio and often contain distinctive vacuolization in their cytoplasm. Furthermore, unlike in dysplasia, mesenchymal cells showing similar changes may also be present in the lamina propria, as well as other characteristic stromal changes of chemotherapy or radiotherapy (Fig. 24.10, A). Therefore, awareness of the patient’s clinical history is critical.

Biopsy specimens from patients with esophagitis caused by GERD or other causes such as drug effects occasionally contain multinucleated epithelial giant cells, raising the possibility of dysplasia (see Fig. 24.10, B and C).⁵⁹ In these cases, no other cytologic or architectural features of dysplasia are present, and results of special studies for viral inclusions are negative. In inflammation-induced multinucleation, the nucleated squamous cells are typically basal or suprabasal in location and may be increased in number adjacent to areas of ulceration. In contrast, multinucleated virally infected cells (e.g., herpes simplex) are common in the surface epithelium and adjacent to sloughing epithelium.

Prognosis and Treatment

Squamous dysplasia frequently occurs adjacent to invasive carcinoma. For example, 30% of patients with a biopsy diagnosis of high-grade dysplasia show invasive squamous cell carcinoma in subsequent endoscopic resections.⁶⁰ In addition, patients with squamous dysplasia are at increased risk for squamous cell carcinoma on follow-up. In a 13-year follow-up study of patients from China, 106 with low-grade dysplasia and 23 with high-grade dysplasia, those with low-grade dysplasia had a threefold to eightfold increased risk, and patients with high-grade dysplasia had a 28- to 34-fold increased risk for invasive carcinoma.⁶¹ In another study, 15% of patients with low-grade dysplasia progressed to high-grade dysplasia, whereas invasive carcinoma developed in 30% of patients with high-grade dysplasia during an 8-year follow-up period.⁶² However, dysplasia may also regress or disappear, although sampling error certainly may account for a normal finding on follow-up biopsy in a patient with dysplasia in a prior biopsy specimen. Therefore, patients with a diagnosis of squamous dysplasia require thorough endoscopic examination with biopsies, first to exclude synchronous invasive squamous cell carcinoma (particularly if associated with a visible mass lesion or ulceration) and second to detect the development of early invasive tumor on follow-up. Any grade of squamous dysplasia associated with a mass lesion should be considered carcinoma and treated accordingly. Low-grade dysplasia without a mass or associated carcinoma may be managed with repeated biopsies and continued surveillance in most instances. Some endoscopically subtle invasive carcinomas have been reported that apparently arose from low-grade dysplasia, further emphasizing the need for careful endoscopic scrutiny and adequate sampling in patients with any grade of squamous dysplasia.⁶³

Endoscopic mucosal resection or endoscopic submucosal dissection, which permits removal of dysplastic lesions or even early superficial cancers, aids in the diagnosis of early invasive tumors and is performed increasingly in some highly specialized centers. In one study of 87 patients with high-grade dysplasia and 213 patients with early (intramucosal) carcinoma treated with these two techniques, a total of 19 patients (6%) developed recurrences over an 85-month follow-up period. Endoscopic submucosal dissection gave superior results, with no nodal or distant metastases during a 36-month follow-up period.⁶⁰

Squamous cell carcinomas occur in the middle third of the esophagus in 50% to 60% of cases, the distal third in 30%, and the proximal third in 10% to 20%.^39,64 Superficial tumors most commonly appear as mucosal plaques or slightly elevated flat lesions but may also be ulcerated, polypoid, or even grossly inconspicuous. Superficially invasive tumors are more commonly multicentric (as much as 20% of cases) when compared with advanced tumors. This finding may reflect either the presence of synchronous primary tumors occurring in a background of dysplasia or the presence of satellite tumor nodules resulting from intramural metastasis.^52,65

The gross appearance of advanced tumors may be classified as exophytic or fungating (60% of cases), ulcerating (25% of cases), or infiltrative (15% of cases) (Fig. 24.11).³⁹ However, this feature is not a significant prognostic factor. In patients treated with preoperative irradiation or chemotherapy, the tumor may be invisible or perhaps replaced by a shallow surface erosion.

Microscopic Pathology

Superficially invasive tumors consist of irregular, elongated projections of dysplastic epithelium that extend into the lamina propria, muscularis mucosae, or submucosa as isolated cells or clusters of cells with a minimal desmoplastic response. Invasion of mucosal and submucosal lymphatics is not uncommon and is likely to account for the occasional instances of intramural metastasis. Advanced carcinomas spread through the esophageal wall, either with an infiltrative pattern composed of individual small nests of tumor cells or with an expansile (pushing) growth pattern composed of a solid mass of tumor cells with a smooth advancing edge. A prominent lymphocytic infiltrate occasionally surrounds the tumor.⁶⁶

Squamous cell carcinomas show a range of differentiation from well to poor (Fig. 24.12). Well-differentiated tumors show variably sized nests of polygonal epithelioid cells with ample eosinophilic cytoplasm, easily recognizable intercellular bridges, and abundant keratinization (squamous pearls), with relatively few compact basaloid cells. Moderately differentiated tumors account for approximately two thirds of squamous cell carcinomas. They contain a higher proportion of primitive basaloid cells than well-differentiated tumors, and they are typically arranged in irregular nests and trabeculae with only focal keratinization. Poorly differentiated tumors show no evidence of keratinization, grow in solid sheets or as single cells, and may contain large, bizarre pleomorphic cells. Squamous cell carcinomas commonly show varying degrees of differentiation within a single tumor. Focal glandular or mucinous differentiation occurs in as much as 20% of cases.^67,68 If the glandular and squamous components of the tumor are comparable in proportion but intimately mixed, it qualifies as an adenosquamous carcinoma (see Carcinoma with Mixed Squamous and Glandular Elements). Focal neuroendocrine or small cell differentiation has also been reported.⁶⁹

Special studies are rarely required to establish a diagnosis of conventional squamous cell carcinoma but may be useful in small biopsy specimens or when rare tumor cells are present, such as for patients who have received neoadjuvant chemoradiotherapy. By immunohistochemistry, squamous cell carcinoma cells are positive for broad-spectrum anticytokeratins and for cytokeratins 13, 14, 18, and 19.^70,71 CK7 reactivity is present in as much as 29% of cases, but most cases are negative for both CK7 and CK20.⁷² In addition, most tumors express the nuclear antigen TP63, similar to squamous cell carcinomas that arise in other sites of the human body.⁴⁹ Mucin stains may show focal positivity in a high proportion of cases, but this finding alone should not imply that the tumor is an adenosquamous carcinoma. Focal positivity for neuroendocrine markers, such as chromogranin and synaptophysin, also does not exclude a diagnosis of squamous cell carcinoma if it is present in a minority of the tumor cells and if the tumor is otherwise morphologically typical of a squamous cell carcinoma and does not show areas of small cell carcinoma.⁷³

Differential Diagnosis

In small, poorly oriented biopsy specimens, distinguishing between in situ neoplasia (dysplasia) and invasive squamous cell carcinoma may be difficult. Squamous dysplasia, unlike invasive carcinoma, displays smooth-edged papillations with a continuous basement membrane and a connection to the surface epithelium and lacks single-cell infiltration, the presence of irregular discontinuous nests of cells, and desmoplastic stroma. However, the diagnostic criteria for squamous cell carcinoma differ between Western and Japanese pathologists, and many lesions that would be considered “high-grade dysplasia” by Western pathologists are diagnosed as “carcinoma” by Japanese pathologists solely on the basis of nuclear features.⁷⁴

Invasive squamous cell carcinoma must also be distinguished from non-neoplastic lesions such as pseudo­epitheliomatous hyperplasia and pseudodiverticulosis. Pseudoepitheliomatous hyperplasia, similar to other reactive squamous proliferations, does not show significant nuclear pleomorphism, loss of polarity, or overlapping of nuclei and always reveals a connection to the surface epithelium (see Fig. 24.8). Reactive lesions do not show desmoplasia. Pseudodiverticulosis is a rare condition that produces numerous islands of reactive squamous epithelium in the mucosa and submucosa, some of which may be irregular in shape, simulating a carcinoma (Fig. 24.13).⁷⁵ This condition is caused by extensive squamous metaplasia of the esophageal ducts and glands, which may occur in association with strictures or motility disturbances. On radiologic examination, pseudodiverticulosis may mimic carcinoma by showing irregular stricture formation. Identifying characteristic diverticula with a barium swallow procedure helps separate this condition from carcinoma radiologically. Pathologically, these lesions are distinguished from invasive carcinoma by the lack of an infiltrative growth pattern, absence of histologic features of dysplastic squamous epithelium, and the presence of smooth, often rounded, islands of reactive squamous epithelium associated with, or replacing, the submucosal glands and ducts with a prominent inflammatory infiltrate.

Biopsy or resection specimens from patients who have been treated with neoadjuvant chemoradiotherapy may contain only scattered atypical cells, which can occasionally make it difficult to distinguish residual carcinoma from reactive mesenchymal cells. Carcinoma cells may be identified by positive immunostaining for cytokeratins and an increased N : C ratio; reactive mesenchymal cells are typically cytokeratin negative and have expanded, often bubbly or “wispy” cytoplasm. Typically, the N : C ratio of these cells is maintained.

Poorly differentiated tumors may be difficult to recognize as squamous in phenotype, and melanoma or even lymphoma may be suspected on morphologic grounds. Positivity for cytokeratins and negativity for melanocytic and lymphoid markers may help eliminate these alternative diagnoses. In some patients, pulmonary squamous cell carcinoma involves the esophageal wall by metastasis or direct extension (see later discussion) and may be confused with a primary esophageal tumor. Adjacent squamous dysplasia provides strong evidence for an esophageal origin of the tumor. In addition, approximately 10% to 20% of lung squamous cell carcinomas show nuclear immunostaining for thyroid transcription factor 1 (TTF-1), which is not expressed in esophageal epithelium or in tumors derived from it.⁷⁶

Prognosis and Treatment

Squamous cell carcinomas may spread horizontally, but more typically they invade vertically through the esophageal wall and in this manner spread to involve contiguous organs such as the trachea, aorta, and pericardium. Intramural metastasis was detected in as much as 7% of resection specimens in one study.⁷⁷ Regional lymph node metastasis is present in approximately 60% of patients at the time of diagnosis, and the lymph node positivity rate correlates with depth of invasion (<5% for intramucosal carcinomas and as much as 45% for submucosal carcinomas).^64,78 Carcinomas originating in the upper thoracic esophagus are more likely to metastasize to cervical or upper mediastinal nodes, whereas tumors from the middle and lower thirds of the esophagus metastasize to lower mediastinal or perigastric nodes.^39,64 However, skip nodal metastases are not uncommon in esophageal cancers. Distant metastasis, which most frequently involves the lung or liver, is present in as much as 60% of patients at autopsy.⁷⁹

Overall, the 5-year survival rate for patients with squamous cell carcinoma is only 10%, but it approaches 30% to 40% for patients treated with esophagectomy.^39,80,81 The most significant prognostic factor is tumor stage, which is based on the American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) classification system (Table 24.3).^81,82 Patients with tumors that penetrate into the submucosa have 5-year survival rates in the range of 60% to 75%, compared with 40% to 60% and 25% to 30% for patients with tumors that extend into the muscularis propria and the adventitia, respectively.^81,83 The presence of lymph node metastasis and a greater number of positive lymph nodes are also correlated with worse prognosis.⁸⁴ In patients who have received neoadjuvant chemoradiotherapy, the presence of residual tumor is correlated with reduced survival. In one study of 175 patients, 55 (31%) had complete histologic tumor response; their median survival time was 125 months, compared with 21 months for those who had residual tumor.⁸⁵ Some authors have also found that poor tumor differentiation is an independent prognostic factor,^80,86 and tumor differentiation as well as tumor location are now incorporated into the AJCC staging for this tumor type (see Table 24.3). Intramural metastases⁷⁷ and lymphovascular invasion⁸⁷ have also been found to be predictive of regional lymph node metastasis and poor survival in some studies, but these findings need to be tested in a prospective manner.