Pulmonary well-differentiated fetal adenocarcinoma with platelet-derived growth factor receptor (PDGFR)α expression

Abstract

Well-differentiated fetal adenocarcinoma (WDFA) is a rare pulmonary malignancy. Biomarkers of tumor biology has rarely been studied in WDFA. Here, we report two WDFA patients. Both patients had blood-streaked sputum or mild hemoptysis at presentation. They underwent lobectomy and systematic mediastinal lymphadenectomy. Expression of PDGFRα on the plasma membrane was demonstrated by immunohistochemistry (IHC) in the resected tumor specimens. Further IHC examination showed intense immunostaining of β-catenin in both patients but negative staining for TP53, CEA, CD56, EGFR, CK5/6, HER2, S-100, ER, PR, BCL2, and NSE. Both patients had no recurrence to date after more than 3 years of follow up. Herein, we reviewed this rare disease with special emphasis on the clinico-pathological features, treatment and potential role of PDGFRα.

Keywords: :

• PDGFRα
• WDFA
• lung cancer
• surgery
• well-differentiated fetal adenocarcinoma
• β-catenin

Introduction

Well-differentiated fetal adenocarcinoma (WDFA) is a rare type of lung cancer. It is characteristically composed of fetal type glands and tubules. The normal stromal components lack sarcomatous feature, which is different from the conventional pulmonary blastoma.^1,2 WDFA is considered a variant of invasive adenocarcinoma in modern classification of lung adenocarcinomas but usually with good prognosis.³

The PDGFR-PDGF signaling system includes two cell surface receptors (PDGFRα and PDGFRβ) and several ligands (PDGFA, PDGFB, PDGFC, and PDGFD). Ligand binding induces receptor dimerization, enabling autophosphorylation of specific tyrosine residues and subsequent recruitment of signal transduction molecules.⁴ PDGFRα, one of the isoforms of platelet-derived growth factor receptor (PDGFR), is a trans-membrane tyrosine kinase receptor with an important role in cancer growth in several tumor types and a small subset of NSCLCs.^5,6 In this study, we report two WDFA patients with positive PDGFRα expression and discuss the clinico-pathological features, treatment and potential role of PDGFRα.

Results

A 25-year-old male patient was referred to the Department of Thoracic Surgery, the First Affiliated Hospital of Sun Yat-sen University for reports mild left chest pain and expectoration of blood-streaked sputum. The patient had no respiratory distress, dyspnea, cough, or wheezing. There was no history of smoking, and the family history was noncontributory. Physical examination was unremarkable. CT of the chest showed a mass measuring 5.6 cm in its greatest diameter in the left lower lobe; there was no mediastinal lymphadenopathy, pleural effusion, or any signs of invasion to the chest wall (Fig. 1A). CT of the head, abdomen and pelvis and radionuclide bone scintigraphy scan revealed no abnormal findings. The patient underwent lobectomy of left lower lobe and systemic mediastinal lymph node dissection in February 2009. The pathological stage was T2bN0M0 (stage IIA) according to the updated staging system of lung cancer.

Figure 1. Chest CT. (A) Case 1. There is a homogeneous peripheral mass in the left lower lobe of lung (white arrows). (B) Case 2. There is a 3.6-cm popcorn-like hilar mass located in the left upper lobe of the lung (white arrows).

Microscopically, the tumor was composed of irregular ductal and papillary proliferation of cuboidal or columnar tumor cells which were predominantly arranged in large flat sheets, morphologically resembling the fetal lung (Fig. 2). The majority of the stromal cells were spindle-like cells without malignant findings. The nucleoli were indistinct, and the mitotic activity was very low. Some of the cells had prominent subnuclear and supranuclear cytoplasmic vacuoles. Squamoid-appearing morules were also identified, intimately admixed with the glandular component (Fig. 2).

Figure 2. H&E staining of two samples. (A) H&E stained section from the surgical resections showed well-differentiated glands and scant stroma. The glands were consisting of irregular tubular structures lined with pseudostratified columnar epithelium, and typical squamoid morules (White arrows) were found. (B) The stroma consisted of cytologically bland fibroblast-like spindle cell without sarcomatous features. The subunclear and supranuclear vacuolization was occasionally observed (Black arrows).

The other patient was a 51-year-old man, who admitted was to our hospital with reports of cough and mild hemoptysis. CT scan of the chest showed a solitary 3.6-cm mass in the left upper lobe of the lungs (Fig. 1B). There was no pleural effusion, mediastinal or hilar lymphadenopathy. The patient underwent a left upper lobectomy with systematic mediastinal lymphadenectomy in November 2008, and the tumor was pathologically staged as T2aN0M0, stage IB. The resected tumor showed classic histologic features of WDFA, i.e., a well-differentiated glandular component showing perinuclear vacuoles and squamous morule formation, and a delicate fibrous stroma containing cytologically normal spindle cells (Fig. 2).

In normal lung tissues, PDGFRα is usually not detectable by immunohistochemistry, and the staining pattern of PDGFRα in lung tumors is at the plasma membrane and in the cytoplasm.⁷ By immunohistochemistry (IHC), we found moderate staining for PDGFRα at the plasmalemma and cytoplasm of tumor cells in these two WDFA cases and negative expression of PDGFRα in the adjacent normal lung tissues (Fig. 3). The tumors also showed intense immunostaining for β-catenin but negative staining for TP53 and CEA (Fig. 4). Additionally, we performed immunostaining for CD56, EGFR, CK5/6, HER2, S-100, ER, PR, BCL2 and NSE. All these tumor markers showed negative staining (data not shown).

Figure 3. PDGFRα staining in two cases. (A) PDGFRα staining showed positive staining at the plasmalemma of the glandular cells. (B) Adjacent lung tissues of tumors in two cases showed negative expression of PDGFRα. Representative photomicrographs are shown at the original magnification × 400.

Figure 4. Immunohistochemical examination of two samples. (A) Both cases were strong positive for the β-catenin staining in the nuclei and cytoplasm. (B) CEA examination showed negative staining in two samples. (C) Negative staining of p53 in immunohistochemical examination. Representative photomicrographs are shown at the original magnification × 400.

Both patients had uneventful postoperative recovery. After more than three years of follow up, both patients have no recurrence to date.

Discussion

WDFA is a subtype of pulmonary blastoma, which was first described by Kradin et al. in 1982. It is a rare lung tumor with an incidence less than 0.1% of that for lung cancers.^1,8 WDFA is defined by a monophasic carcinoma solely consisting of malignant epithelial components (squamoid morules) with subnuclear and supranuclear vacuoles, and a benign-appearing mesenchymal stroma.^1,9,10 Recently, WDFA is classified as a variant of invasive adenocarcinoma according to its predominant component the malignant glandular structures.³ However, it is a low-grade fetal adenocarcinoma with a favorable clinical outcome.

PDGFs are a growth factor family; they exert their mitogenic effects through PDGFRα and PDGFRβ tyrosine kinase receptors. Activation and autophosphorylation of the tyrosine kinase domain of PDGFR recruits SH-2 domain-containing signal transduction proteins to activate downstream pathways through SRC, PI3K/AKT/mTOR¹¹ and phospholipase C¹² and promote oncogenic transformation.¹³ Recent studies revealed that high expression of PDGFRα was associated with shorter patient’s survival in gastroenteropancreatic neuroendocrine tumors¹⁴ and high metastatic potential of medulloblastoma cells.¹⁵ However, the role and involvement of PDGFRα expression in WDFA as a prognostic factor has not been studied. In addition to its prognostic role, PDGFR is also an important target for chemotherapy treatment. Inhibition of PDGFRα signaling disrupts cancer cell survival in the subset of GISTs with activating PDGFRα mutations.^16,17 The efficacy of targeted disruption of PDGFRα signaling using small molecular tyrosine kinase inhibitors in recurrent or metastatic WDFA expressing PDGFRα remains to be investigated in the future. Given the potential role of PDGFRα in the prognosis and targeted therapy in the above cancers, the value of PDGFRα in prognosis and guidance of therapy for WDFA should be further evaluated.

Little specific biomarker information has been reported for this rare tumor. Lineage-specific transcription factors (TTF-1 and GATA-6) were associated with fetal lung epithelial morphogenesis in WDFA.¹⁸ Lori et al. reported that aberrant nuclear/cytoplasmic expression of β-catenin, which was involved in both cadherin-mediated cellular adhesion and intracellular signaling in the WNT pathway,^19,20 had diagnostic utility for WDFA. The cases we reported also showed strong immunoreactivity with β-catenin. The molecular biomarkers reported for WDFA are summarized in Table 1.

Table 1. Summary of molecular biomarkers reported in WDFA

Reports	Molecular biomarkers	Findings
Nakatani Y^19	β-catenin	Overexpression and aberrant nuclear/ cytoplasmic localization of β-catenin have a potential diagnostic role of WDFA.
Yamazaki K^18	TTF-1, GATA-6	TTF-1 and GATA-6 may partially and incompletely simulate fetal lung epithelial morphogenesis.
Current study	PDGFRα	PDGFRα may be a potential target in WDFA.

The standard treatment for WDFA is surgical resection, and most of the reported cases were in stage I with a 5-y mortality rate of 10–20% after complete resection.^2,10 Postoperative chemotherapy or radiotherapy are selectively used for patients with advanced lung cancers, but the potential benefits in WDFA are unclear. We reviewed 9 cases of WDFA with complete resection, reported between 1995 and 2012, 6/9 were in staged I and II.^8,21,22 Among the 6 cases, 1/6 (IIB) received adjuvant chemotherapy (carboplatin and paclitaxel), 5/6 received no adjuvant therapy after complete resection, and all of them had a good prognosis.^8,21,23-27 The two cases reported here were in stage IIA and IB, and no other treatment was performed after surgical resection. Up to now, no recurrence or metastasis has occurred. We speculate that adjuvant therapy may be unnecessary for patients with stage I and II WDFA after complete resection. Nevertheless, for WDFA patients with more advanced diseases or recurrent diseases, the expression and activation of PDGFRα may suggest that they may benefit from therapies targeting PDGFRα.

In summary, WDFA is a rare lung cancer with good prognosis, and complete surgical resection is still the primary therapy for this disease. The biomarkers, such as β-catenin, PDGFRα, need to be further investigated for potential contribution to preoperative diagnosis and targeted therapy in WDFA.

Patients and Methods

The two patients in this report were diagnosed of WDFA by pathologists in our hospital. The study was approved by the Committee for the Conduct of Human Research and Institutional Review Board of the First Affiliated Hospital of Sun Yat-Sen University, and informed consent was obtained from each patient.

Immunohistochemistry (IHC) was performed as previously described.²⁸ Formalin-fixed lung tissues and tumor tissues were embedded in paraffin and cut by microtome into tissue sections (4-μm thick) for immunostaining according to standard techniques. The primary antibodies were rabbit polyclonal antibody against PDGFRα (Santa Cruz Biotechnology, Inc.), monoclonal mouse antibody against β-catenin (Dako North America, Inc.), monoclonal rabbit antibody against p53 (Dako North America, Inc.) and monoclonal mouse antibody against CEA (Dako North America, Inc.). All other antibodies were from Dako Technology. As negative controls for non-specificity of the antibody for PDGFRα, immunostaining was performed for each specimen by omitting the primary antibody in the procedure. Subjective assessments of the intensity of staining were performed according to the manufacturer’s package insert.

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

No potential conflicts of interest were disclosed. The work was supported by grants from China National Natural Sciences Foundation (NO.30801136 to C. Cheng) and (No.81171125 to C. Cheng) and the Research and Development Program of Sun Yat-sen University (10YKPY09 to C. Cheng).

Supplemental Materials

Supplemental materials may be found here:

http://www.landesbioscience.com/journals/cbt/article/22253/