Primary pulmonary invasive mucinous adenocarcinoma (IMA) is an adeno-
carcinoma variant according to the current World Health Organization (WHO) classification of lung tumors [11], formerly known as mucinous bronchioloalveolar carcinoma (BAC), which is relatively rare [3]. IMA has a range of differences from those of invasive non-municous adenocarcinoma (INMA), including genetic, clinical, radiological and pathological characteristics. The age of IMA patients ranged between 41 and 66 years and the majority were non-smoking females [12]. Clinical features are generally non-specific, such as cough, fever, expectoration and dyspnea etc. The symptom of coughing with white sputum may help early diagnosis of pneumonic-type adenocarcinoma[13]. In the present study, it was revealed that the patient was female and non-smoker, as well as mild coughing with white sputum when she was initially diagnosed, which were consistent with previous study[13].
IMC displays a variety of radiological presentations. According to the CT findings, IMC has been classified into three patterns[14]: ① solitary nodules or masses; ②localized consolidation, pneumonic types; ③multicentric or diffuse disease, most patients have a mixture of these features. The most common features on chest high-resolution computed tomography (HRCT) scan are predominant ground- glass opacities, consolidations, or multiple nodules[15]. Because of the nonspecific
radiographic findings, we may usually not differentiate them from other lung diseases, such as atypical pneumonia, tuberculosis, pulmonary lymphoma or metastatic lung cancer[15, 16]. However some studies [17–19] reported that the pneumonic types IMA had air bronchograms with stretched, sweeping, narrowed appearance and bulging of the interlobar fissure. In our report, the patient was initially misdiagnosed as focal organizing pneumonia, but after ten days of anti-inflammatory therapy, the lesions are not eliminated, ultimately we got an accurate diagnosis by percutaneous computer tomography (CT)-guided lung biopsy. we reviewed her chest CT imagings carefully, some signs were found, such as air bronchograms with a stretched, sweeping and bulging of the interlobar fissure, which can help the differential diagnosis. Percutan- eous computer tomography (CT)-guided lung biopsy appears to be an effective way to make a definitive diagnosis.
Almost 50% of non-small-cell lung cancer (NSCLC) patients present with metastatic disease at the time of diagnosis, the most common NSCLC metastatic site is bone (34%), followed by lungs (32%), brain (28%), adrenalglands (17%), liver (13%), and extrathoracic lymph nodes (9%) [8]. Colonic metastasis is extremely uncommon with an incidence of 0.1% [20], and about 50 unique case reports of lung cancer metastasizing to the colon have been published globally[4, 6–8, 10, 21–70], among them, squamous cell carcinoma(SqCC), lung adenocarcinomas, small cell lung carcinomas, Large-cell carcinoma, other primary lung histopathologic cell types such as sarcomatoid, pleomorphic, and unknown were confirmed as primary origins, SqCC is the most common origins, followed by lung carcinoma.
Immunohistochemistry is very valuable for determining the primary origins. Among those, CK7, CK20, CDX2, and TTF-1 has been proven to be diagnostic[6]. Most pulmonary adenocarcinomas are typically positive for TTF-1 and CK 7, and negative for CK 20[71–74]. Most colorectal adenocarcinomas are negative for TTF-1 and CK 7, and positive for CK 20[75–76]. However, up to 20% of lung adenocarcin- omas are reported to be negative for TTF-1, and up to 30% may react positively with CK 20. Several studies showed CDX-2 to be highly sensitive for colorectal ACA, but among lung tumors, only a rare type of pulmonary ACA, the goblet cell variant of primary mucinous (so-called colloid) ACA, has been reported to be positive for CDX-2[77]. TTF-1 is expressed only in lung cancer and thyroid cancer [77– 81]. The expression of TTF-1 rate in IMA is often lower than that in non-mucinous adenocarc- inoma. In addition, according to the report of Su et al [12], the positive rates of primary lung adenocarcinoma were 73% for TTF-1, 75% for CK7, and 0% for CK20, the positive rates of primary colon cancer were reported to be 0% for TTF-1, 7% for CK7, and 86% for CK20. Thus, since TTF-1 expression is lacking in all adenocarci- noma types except for lung adenocarcinoma, which is very important to distinguish between primary adenocarcinoma and metastatic adenocarcinoma.
KRAS mutations are the most requent oncogenic driver mutations in IMAs (up to 86%) [82, 83]. the most common types are G12D and G12V in IMAs [83]. KRAS mutation has been reported to be associated with invasive mucinous adenocarcinoma, formerly known as mucinous BAC [84]. For our patient, the lung lesion was immun- oreactive for CK7, favoring the diagnosis of lung adenocarcinoma. Negative staining of p63 rules out squamous cell carcinoma of the lung. KRAS mutation (p.G12 D mutation) was positive. The sigmoid lesion was immunoreactive for TTF-1, CK 20, CDX2. The positive expression of TTF-1 indicated that her sigmoid tumor was metastatic from pulmonary carcinoma. Because of the primary pulmonary mucinous adenocarcinoma, CDX2 can be positive. These IHC stains can help determine the primary tumor and distinguish metastatic carcinoma from primary tumor.