Adenoid cystic carcinoma of the right main bronchus showing squamous differentiation and mimicking mucoepidermoid carcinoma: a case report

Abstract

Complete dissection of tracheobronchial adenoid cystic carcinoma (TACC) by surgery alone is sometimes difficult and has a greater propensity than tracheobronchial mucoepidermoid carcinoma (TMEC) for its surgical margin to become positive. In addition, TACC is more likely to present distant metastases than TMEC. Considering these facts, TACC and TMEC should be differentiated based on histopathological examination of biopsy specimens. Herein, we present a case of 54-year-old woman with a tumor in the right main bronchus, whose biopsy specimen was difficult to diagnose as TACC or TMEC. The specimen from the rounded protrusion of the tumor showed squamous differentiation, along with the presence of glandular and basaloid cells, making morphological examination alone ineffective in rendering a definite diagnosis. Thus, the addition of immunohistochemical analysis, αSMA and CD43 expression in basaloid cells and c-kit expression in glandular cells, was useful for accurately diagnosing TACC in this case. The squamous component was considered to be neoplastic because of its increased expression of cyclin D1 and overexpression of p16. The surgically resected specimen contained typical morphology of ACC, and the diagnosis of TACC was definitely confirmed.

Keywords: Bronchus; adenoid cystic carcinoma; immunohistochemistry; mucoepidermoid carcinoma; squamous differentiation.

Figure 1

Bronchoscopy. A. A rounded protrusion almost occluded the right main bronchus. B. Following radiation therapy, the opening of the right main bronchus was observed.

Figure 2

Contrast-enhanced computed tomography. A, C. Axial; B, D. Coronal. A, B. Moderately enhanced tumor was located in the right main bronchus. C, D. Following radiation therapy, a significant reduction of tumor size was observed.

Figure 3

Microscopic and immunohistochemical findings of a biopsy specimen. A. A mixed squamous and glandular lesion is observed (×20). Inset: true gland lined by glandular cells and pseudogland lined by basaloid cells (×400). B. Periodic acid-Schiff-alcian blue (PAS-AB) staining shows PAS-positive glycogen in the region with squamous cells (arrow heads) and an AB-positive pseudoglandular structures (arrows) (×20). Inset: some true glands are PAS-positive in contrast to the AB-positive pseudoglandular structures (×400). C. True glands (arrows) are surrounded by monolayer to multilayer basaloid cells. These complexes are continuous each other and gradually transit to the surface squamous cells (×400). Asterisks indicate pseudoglands. D. Positivity of basaloid cells and squamous cells for p63 (×400). E. Positivity of basaloid cells for αSMA (×400). F. Positivity of basaloid cells for CD43 (×400). G. Positivity of c-kit for the majority of the glandular cells, and focally for basaloid cells (×400). H. Increased immunoreactivity of cyclin D1 in glandular and squamous cells, with lesser reactivity to basaloid cells (×400). I. Overexpression of p16 in glandular and squamous cells with lesser reactivity to basaloid cells (×400).

Figure 4

Gross findings of a surgically resected specimen. The surgically resected specimen reveals a whitish lesion centered in the right main bronchus, with spreading along the bronchial tree.

Figure 5

Microscopic findings of a surgically resected specimen. A. Remnant of the rounded protrusion is observed (×12.5). B. Most of the tumor cells inside the protrusion are non-viable, with increased cytoplasmic eosinophilia and nuclear pyknosis; tubular or cribriform pattern of growth is speculated (×200). C. Viable tumor cells are observed, with tubular or cribriform growth pattern (right side of the micrograph); non-viable tumor nests are present (left side of the micrograph) (×100). Inset: typical cribriform growth pattern observed in the viable tumor component (×400).