Diagnosis Discrepancy from Different Original Specimen in PCR EGFR Mutation Test

Epidermal growth factor receptor (EGFR) mutation status guides treatment in non-small cell lung cancer; del E746-A750 in exon 19 and p.L858R in exon 21 are the most common mutations. We present a patient whose initial lymph node and computed tomography-guided pathology led to a suspicion of poorly differentiated carcinoma; however, during the clinical course, no obvious tumor origin was noted, and the pathologic morphology favored the squamous type. Not until the EGFR mutation status of secondary sites was checked did we confirm the disease origin as the lung.


Introduction
Somatic mutations in the epidermal growth factor receptor (EGFR) gene have guided treatment of non-small cell lung cancer based on the response of EGFR to specific kinase inhibitors [1,2]. A recent study also described some EGFR mutations that were observed in nonadenocarcinoma lung cancer [3]. Further, EGFR mutation status has been explored in other types of cancer [4]. However, the treatment response is still not reliably predicted by mutation status. Even with this molecular diagnostic tool, clinical decisions are largely based on the patient's clinical presentation.

Case Report
A 52-year-old Chinese woman with a history of uterine myoma 10 years after an abdominal total hysterectomy and a T11 compression fracture from a traumatic fall underwent polymethyl metamethacrylate vertebroplasty. Post-surgery, she experienced ongoing dyspnea, and x-ray imaging showed massive right side pleural effusion. The thoracocentesis and pleural effusion led to a suspicion of adenocarcinoma, but her EGFR mutation status was negative. The initial evaluation of tumor markers revealed only mild CE-153 elevation (CEA: 2.0 and CA-153: 43.6). A chest computed tomography (CT) scan showed that metastatic carcinoma with right side pleural seeding, massive right side pleural effusion, and as well as bone and liver metastases.
For confirmation of the malignancy, pathological analysis of her lymph nodes, CT-guide liver biopsy was arranged, and the results showed poorly differentiated metastatic carcinoma. EGFR mutation test of the lymph node specimen by polymerase chain reaction (PCR) was done but showed negative. Pathology report of lymph node demonstrated CK(+), CK(7), TTF-1(-), CK20(-), ER(-), PR(-), and HER(-), there for no definite cancer origin can be made.
Sonography of her abdomen and a breast echocardiogram to survey for malignancies were negative. Later she developed massive right pleural effusion and had a pigtail catheter inserted times. Thoracoscopic surgery for chest tube insertion and pleural biopsy were arranged. Pathology report of pleural biopsy still presented poorly differentiated carcinoma.
We repeated the EGFR mutation analysis by PCR from the pleural biopsy specimen, confirming the presence of the p.L858R mutation in exon 21. Repeat tumor marker analysis showed the following results: CEA, 1.9; CA-153, 245.4; CA-125, 754.5; and C1-199, 73.8.
After the diagnosis was confirmed, we prescribed the tyrosine kinase inhibitor (TKI), erlotinib. After one month of treatment, she had stable x-ray findings. However, her dyspnea progressed, she had a fever on and off, and her sputum culture confirmed Acinetobacter baumannii pneumonia. The patient died due to hypoxia and hypercapnia. Our result suggested that EGFR mutation should be done on the primary origin in addition to the metastatic site (Figures 1 and 2).

Discussion
EGFR is the cell-surface receptor for members of the epidermal a. b.
c. d. growth factor family of extracellular protein ligands [5]. Mutations affecting EGFR expression have been related to cancer formation. In the past decade, the superior response of pulmonary adenocarcinoma with EGFR mutations to TKIs has changed the treatment guidelines, especially for elderly patients and those with locally advanced or metastatic pulmonary adenocarcinoma [6]. More recent research has also confirmed the presence of EGFR mutations in other types of lung cancer [7] and in triple negative breast cancer [4]. However, the EGFR mutation rate is extremely low in non-adenocarcinoma NSCLC. The treatment response of other EGFR mutation-positive cancer types was described in the OPTIMAL study [8]. In most hospitals, EGFR mutations are detected with mutation-specific IHC; however, the quality of the sample and the number of cancer cells greatly impact the quality of the result. Using commercially available monoclonal antibodies, the specificity may be increased to 99.8%, but the sensitivity is variable [9,10]. The two most common mutations are del E746-A750 in exon 19 and p.L858R in exon 21 [11], which account for up to 80% to 90% of all mutations [12]. However, these mutations are rarely observed in other malignancies. In our patient, we assumed that the negative EGFR mutation result was due to inadequate specimen quality. Due to the persisting massive pleural effusion and clinical features consistent with adenocarcinoma, we reexamined the EGFR mutation status in the pleural biopsy specimen and detected the commonest p.L858R mutation.
We have no data to confirm that the metastatic site had the same EGFR mutation as the primary site or that all of the tumor tissue had the same EGFR mutation. In patients with multiple metastases, it is important to check the EGFR mutation status of the primary site.

Conclusion
Determining the EGFR mutation status is essential in the diagnosis and treatment of pulmonary adenocarcinoma, but an adequate and high-quality sample is essential. In some cases, repeat testing may be indispensable to establish the correct diagnosis.