Collision Tumor of Metastatic Rectal Cancer and Primary Lung Adenocarcinoma Presented as an Isolated Pulmonary Nodule

Abstract

INTRODUCTION: We describe here a unique case of collision tumor of metastatic rectal adenocarcinoma and primary pulmonary adenocarcinoma, in which the two components were juxtaposed to each other and presented as an isolated pulmonary nodule CASE PRESENTATION: The patient is a 60-year-old female non-smoker who was conducted Dixon surgery for rectal adenocarcinoma in our hospital four months ago. She denied any complains of coughing, wheezing and chest pain. During her postoperative follow up, the serum carcinoembryonic antigen (CEA) level was slightly declined from 113.08 preoperatively to 101.40ug/l. Serum CA19-9 was fallen from 41.40U/ml to normal range. However, follow up investigations 4 months postoperatively showed an newly-developed solitary pulmonary nodule at computed tomography scan (CT) which presented an approximate 3cm lobulated and spicular-circumscribed ground-glass opacity containing slightly-enhanced solid component with air bronchogram in the right lower lung (Fig.1). A CT-guided fine needle aspiration biopsy suggested a primary pulmonary adenocarcinoma. Then the patient underwent right lower lobectomy and mediastinal lymph node dissection. A histopathologic analysis confirmed a diagnosis of collision tumor of metastatic rectal adenocarcinoma and primary pulmonary adenocarcinoma with an interlobar lymph node metastasis. Histologically, the tumor was composed of two components, a pulmonary adenocarcinoma and a metastatic rectal adenocarcinoma. The pulmonary adenocarcinoma accounted for 90% of the total tumor distribution, while a metastatic rectal adenocarcinoma accounted for a very small area measuring 0.3cm A- 0.2cm. The pulmonary adenocarinoma consisted of well-differentiated adenocarcinoma showing a lepidic pattern in which alveolar septa were lined by relatively uniformed malignant pneumocytes . The metastatic rectal adenocarcinoma consisted of columnar cells arranged in an acinar or gland pattern with central necrosis (Fig.2C). The two components were juxtaposed to each other without transition in between. Immunohistochemistry (IHC) was performed on paraffin-embedded sections using the standard EnVision method. The pulmonary adenocarcinoma component was strongly positive for CK7 and TTF-1 but was negative for CDX2 and CK20. The metastatic rectal adenocarcinoma component was positive for CDX2 and CK20 but was negative for CK7 and TTF-1 DISCUSSION: Since imaging and/or laboratory examination cannot differentiate primary lung tumor from metastatic tumor, the history of malignant disease and pathological comparison with the patienta(euro)(trademark)s prior histological sections are reliable for the diagnosis of this entity. In the present case, metastatic rectal adenocarcinoma should be distinguished from primary pulmonary adenocarcinoma with enteric differentiation. It is still difficult to distinguish between primary pulmonary adenocarcinoma with enteric differentiation and secondary colorectal adenocarcinoma due to the similar morphology. Utilizing immunohistochemistry staining may be the only reliable method for differentiating the metastatic lesion from primary one. CK20 and CDX2 are positive in almost all colorectal carcinoma but is also detectable in fewer than 10% of primary lung adenocarcinoma (especially cases of adenocarcinoma with enteric differentiation). TTF-1 is expressed in the majority of lung adenocarcinoma and nearly all thyroid adenocarinoma but is rarely seen in colorectal adenocarinoma. CK7 is also expressed in the majority of lung adenocarcinoma but is negative in colorectal adenocarcinoma. In the present case, the metastatic rectal adenocarcinoma was positive for CDX2, CK20 but was negative for CK7 and TTF-1, suggesting the lesion was metastatic. Molecular signatures are also helpful to differentiate metastatic from primary tumor. In the present case CONCLUSIONS: In conclusion, we descried a rare case of cancer-to-cancer metastasis of metastatic rectal adenocarcinoma and primary pulmonary adenocarcinoma, in which two components were juxtaposed to each other and presented as an isolated pulmonary nodule.