Transition From Distinct Types of Mutation-Harboring Multifocal Lung Adenocarcinoma to Rhabdoid Tumor: A Longitudinal Follow-Up

Background

Rhabdoid tumor (RT), a highly aggressive neoplasm, was first described in 1978 as a childhood-onset distinctive renal tumor [1]. Several cases of adult-onset RTs have been reported in the kidneys as well as extrarenal sites including the lungs [2,3]. In the 2004 World Health Organization (WHO) classification, large-cell carcinoma with rhabdoid phenotype (LCC-RP) was grouped as a variant type of large-cell carcinoma [4]. LCC-RP is defined as having malignant tumor cells comprised of ≥10% rhabdoid cells, which are characterized by abundant acidophilic cytoplasm, large nuclei, and conspicuous eosinophilic cytoplasmic globules [5]. LCC-RP is extremely rare, and it is an aggressive malignancy with a poor prognosis [5,6].

In the 2015 WHO classification, the rhabdoid phenotype was regarded as a cytologic feature rather than a specific histologic group, as it colocalizes with various histologic subtypes [7,8]. More recently, SMARCA4 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4)-deficient thoracic sarcomas (SMARCA4-DTSs) were proposed as a distinctive disease entity with rhabdoid morphology and highly aggressive malignancy [9]. To date, direct evidence of the cell lineage in which RTs arise from a specific subtype of lung cancer has not been obtained. The driver oncogene(s) responsible for the occurrence of RT in lung cancer are also not fully understood. Moreover, the distinction between RT associated with subtypes of lung cancer and SMARCA4-DTSs remains to be determined.

Here, we report a patient with RT arising from multifocal lung adenocarcinoma. The results of our longitudinal chest computed tomography (CT) and KRAS mutation analyses demonstrated that the patient’s RT originated from one of the multifocal lung adenocarcinomas. An immunohistochemical study revealed that inactivation of SMARCA4 gene was unaffected in the patient. To the best of our knowledge, this is the first case report in which the emergence of RT within a multifocal lung adenocarcinoma lesion was captured during a sequential chest CT follow-up.

Case Report

A 78-year-old Japanese woman presented with a 1-month history of dyspnea on effort. She had never smoked and had no history of alcohol use or dust exposure. She had a 32-year history of systemic lupus erythematosus, and she had been continuously treated with oral prednisolone (4 mg/day) and mizoribine (50 mg/day). She had undergone radical surgery for ascending colon cancer 4 years before her presentation. The chest CT at presentation demonstrated 3 subsolid nodules in her lung fields: an 11-mm subsolid nodule in the superior (S6) segment of the right lower lobe, a 9-mm subsolid nodule in the superior (S6) segment of the left lower lobe, and an 8-mm subsolid nodule in the anteromedial (S8) segment of the left lower lobe (Figure 1).

A transbronchial biopsy was performed for the lesion in the right S6 segment, but no definite diagnosis was made. The patient was then followed-up by chest CT assessments, and the chest CT examinations conducted 3 and 9 months later showed that the nodules had remained unchanged in size. However, a chest CT at 15 months demonstrated the development of a 37-mm mass lesion in the right S6 segment. A CT-guided needle biopsy was performed for the mass lesion at 16 months. The pathology assessment of the needle-biopsied specimen revealed that the mass lesion was composed of carcinoma cells with rhabdoid features, characterized by large cells with eccentrically located nuclei, prominent nucleoli, abundant eosinophilic cytoplasm, and large intracytoplasmic inclusions. The tumor cells were negative for EGFR mutations and ALK gene rearrangement.

Immunohistochemistry results showed that the programmed death-1 ligand-1 tumor proportion score of the tissue sample was 50%. A chest CT examination revealed the rapid growth of the mass lesion (from 37 mm to 60 mm within 1 month) (Figure 1). The subsolid nodules in the left S6 and S8 segments were unchanged in size throughout the clinical course. At 17 months, the patient was hospitalized with fever, wet cough, bloody sputum, and appetite loss. Her systemic condition deteriorated rapidly, and her Eastern Cooperative Oncology Group performance status fell to 4. We therefore decided to manage her treatment as best supportive care. She died 1 month after being hospitalized.

The autopsy revealed that there was a 65-mm mass lesion in the right S6 segment with extensive hemorrhage and necrosis (Figure 2A). The mass consisted of 90% solid tumor with rhabdoid cells and 10% non-mucinous adenocarcinoma lesion with focal intracytoplasmic mucin (Figure 2B–2D). A continuum of changes from adenocarcinoma to the solid area with rhabdoid cells was observed, suggesting the process of epithelial-mesenchymal transition (EMT) (Figure 2E). The adeno-carcinoma lesion was positive for cytokeratin (CK) AE1/AE3 (a pan-cytokeratin marker), CAM5.2 (a pan-cytokeratin marker), CK7, and CK20 (Figure 3A, 3C, 3F, 3G). Mucin 5AC (MUC5AC) immunopositivity was detected in a small part of the adeno-carcinoma lesion (Figure 3H). The immunoreactivity for hepatocyte nuclear factor 4α (HNF4α) was scant (Figure 3I). Rhabdoid cells were positive for AE1/AE3, CAM5.2, and vimentin but negative for CK7, CK20, MUC5AC, and HNF4α (Figure 3B, 3D, 3E). Multiple metastatic foci of RT were observed in the pancreas, lungs, heart, gall bladder, and soft palate. There were another 2 adenocarcinoma lesions in the S6 and S8 segments of the left lower lobe (Figure 4A–4E). There was no evidence of the recurrence of the preexisting colon cancer.

To investigate whether the adenocarcinomas and RT had the same origin, we analyzed RAS mutation in each tumor lesion by performing an amplification refractory mutation system/ Scorpion PCR assay [10]. The study protocol was approved by the University of Miyazaki Research Ethics Committee (No. C-0040). Informed consent was obtained from the patient’s family. Both tumor components (the adenocarcinoma lesion and the RT lesion) were microdissected from the right S6 specimen.

The RAS mutation analysis revealed the same KRAS mutation, G12D, in both the adenocarcinoma and the RT components in the right S6 mass lesion (Figure 5). The metastatic lesion of RT in the soft palate also had the same KRAS mutation (G12D). The adenocarcinoma lesions in the left S6 and left S8 segments had different KRAS mutations – A59G and G12C, respectively.

We then investigated the involvement of SMARCA4 gene deficiency in the emergence of the RT by evaluating the nuclear expression of SMARCA4 [9,11–14]. On immunohistochemistry, both the adenocarcinoma and the RT components in the right S6 mass lesion retained nuclear expression for SMARCA4 (BRG1; Figure 6A–6C), suggesting that SMARCA4 gene was unaffected in our patient’s case.

Discussion

Rhabdoid tumor of the lung is an extremely rare type of lung cancer characterized by a highly aggressive malignancy property. The origin of RT and its responsible driver oncogene remain unclear. This is the first case report identifying an RT that had originated from a multifocal adenocarcinoma in the lung. The longitudinal CT findings and the results of our KRAS mutational analyses suggest that the multifocal lung adeno-carcinoma was the source of our patient’s RT by activating a mutation in the KRAS gene as its driver oncogene. This patient’s case strongly highlights the necessity for more careful attention during the follow-up of multifocal subsolid nodules in the lungs, in order to detect the occurrence of this highly aggressive malignancy.

Several case studies have reported RTs in the lung that co-localized with various subgroups of differentiated lung cancer. Based on our literature search, as of March 20, 2021, 54 cases of RT in the lung have been described in 22 published articles (Table 1) [5,6,15–34]. Among these cases, 50 case reports noted the associated tumor types: adenocarcinoma (30%, 15 of the 50 cases), large-cell carcinoma (28%, 14 cases), poorly or undifferentiated tumor (10%, 5 cases), sarcomatoid carcinoma (8%, 4 cases), large-cell neuroendocrine carcinoma (6%, 3 cases), squamous cell carcinoma (4%, 2 cases), small cell carcinoma (4%, 2 cases), invasive mucinous adenocarcinoma (IMA, 2%, one case), and more. This is the first case report to describe a patient with RT associated with multifocal lung adenocarcinoma.

Since some of the adenocarcinoma cells contained intracytoplasmic mucin in our patient’s case, we initially considered IMA as a differential diagnosis of non-mucinous lung adenocarcinoma. However, several of the findings were different from the essential and desirable diagnostic criteria of IMA described in the most recent published WHO classification of thoracic tumors [35]. First, almost none of tumor cells in our patient’s case had abundant apical columnar cells with small basally oriented nuclei. Second, the immunopositivity of MUC5AC and HNF4α, which are markers of IMA, was scant in the present case. A recent study with a comprehensive genomic analysis demonstrated the clonal relationship of spatially separate IMA lesions: among 24 patients with 2 separate IMAs, tumors from all but 1 patient shared the same driver mutations [36]. In contrast, in the present study, each adenocarcinoma lesion possessed a different type of KRAS mutation. We thus concluded that all 3 of these adenocarcinomas were not IMAs, but rather were non-mucinous adenocarcinomas with intracytoplasmic mucin.

In our patient’s case, 4 findings indicated that the multifocal adenocarcinoma underwent a transition to RT. First, the histology showed the presence of the continuum of changes from adenocarcinoma to the solid area with rhabdoid cells, suggesting the EMT process. Second, the immunohistochemical study exhibited continuous changes of epithelial- and mesenchymal-marker expression between the adenocarcinoma and RT areas. Third, the KRAS mutation analyses revealed the same KRAS mutation (G12D) in one of the adenocarcinoma components and the RT component in the identical mass lesion and metastatic RT lesion, indicating that all 3 of these components had the same clonality. The different KRAS mutations in each of the 3 adenocarcinoma lesions (G12D in the adenocarcinoma lesion in right S6, A59G in the adenocarcinoma lesion in left S6, and G12C in the adenocarcinoma lesion in left S8) also clearly indicated that the multiple adenocarcinomas in our patient were a bona fide multifocal lung adenocarcinoma. Fourth, the RT arose within one of the multifocal adenocarcinoma lesions during the chest CT follow-up for multiple subsolid nodules. Importantly, all of the reported RT cases in the lung are RTs that were observed at the first presentation. In contrast, at our patient’s initial visit, there were only multiple subsolid nodules (corresponding to adenocarcinoma lesions) and no mass shadow (corresponding to an RT lesion). After the mass shadow appeared, it grew rapidly, reflecting the aggressive phenotype of RT. The emergence and rapid development of RT within the adenocarcinoma lesion were captured in the longitudinal chest CT follow-up. In this respect, our report provides strong evidence that a multifocal adenocarcinoma can actually undergo a transition to RT.

The EMT plays pivotal roles in cancer biology including tumor growth, invasion, dissemination, and metastasis [37]. Since EMT-suggestive findings were observed in the RT specimen in the lung in the present and previous cases [26,31], the EMT might be key to the dedifferentiation of parental cancer cells to rhabdoid cells in the lung. Regarding the mutation responsible for RT evolution, Dettmer et al showed the existence of the same EGFR activating mutation – exon 19 deletion – in both the adenocarcinoma part and the RT part within a single tumor lesion [31]. This finding suggests that these 2 tumor components have the same origin. However, since the EGFR deletion mutation does not induce the EMT by itself [38], it is unlikely that this EGFR mutation directly induces RT emergence. In our patient’s case, we identified the same KRAS mutation, G12D, in both the adenocarcinoma and RT components. We also observed that EGFR gene or ALK gene was the wildtype in the RT lesion in the present case. Because G12D is an activating oncogenic mutation of KRAS, which in turn facilitates a transcriptional program involved in EMT [39,40], we believe that the RT emergence from the adenocarcinoma reported herein was caused by KRAS G12D mutation via the EMT.

In 2015, Le Loarer and colleagues demonstrated that SMARCA4, which encodes an ATPase subunit of BAF chromatin-remodeling complexes, is mutationally inactivated in thoracic undifferentiated malignancies with rhabdoid morphology and aggressive malignancy [9]. They designated this new type of thoracic malignancy ‘SMARCA4-DTS.’ Several research groups then reported cases of SMARCA4-DTSs located in the lung [11–14,41]. We here examined the involvement of SMARCA4 deficiency in the development of RT in our patient, and we observed the retention of nuclear immunoreactivity of SMARCA4 in both the adenocarcinoma and RT lesions. Since all of the reported SMARCA4-DTSs cases demonstrated diminished SMARCA4 expression [11–14,41], we speculated that the SMARCA4 gene in our patient was unaffected. Taking the past and present findings together, we believe that RT associated with subtypes of lung cancer and SMARCA4-DTSs, which are clinically and histologically indistinguishable rhabdoid tumors, are distinct disease entities and have different cell lineages. The fact that all of the SMARCA4-DTSs in the lung in the reported cases demonstrated the absence of a well-differentiated component such as glandular formation and keratinization [11–14,41,42] supports this idea. In addition to the pathogenic understanding, being able to distinguish SMARCA4-DTSs and RT associated with subtypes of lung cancer will be vital for making decisions about treatment, as each malignancy’s respective molecular-targeted therapy could be developed [43,44].

Another important feature of our patient’s case was the rapid growth of the mass during the CT follow-up for the management of the multiple subsolid nodules of the lung. The 2017 Fleischner Society Guidelines recommend that incidental pulmonary nodules be managed as follows: in patients with multiple subsolid lesions ≥6 mm, a short-term follow-up CT at 3–6 months should be considered [45]. Our patient’s case emphasizes the necessity of considering aggressive surgical intervention (eg, multiple limited resections) in patients with multiple subsolid lesions in order to terminate the evolution of the RT.

Conclusions

We present the first case of a rhabdoid tumor arising from multifocal lung adenocarcinoma. KRAS mutation is considered to be responsible for the RT emergence in this patient, via the EMT. We propose that RT associated with subtypes of lung cancer and SMARCA4-DTSs are distinct disease entities. This report indicates that careful management and more aggressive surgical intervention should be considered in the management of multiple subsolid lesions, given concerns about the evolution of this aggressive tumor.