IMT is a rare neoplasm which belongs to a subtype of soft tissue sarcoma, with an overall prevalence of approximately 0.04%-0.7% (13, 14)
It may occur at any age but it is more common in children and adolescents, constituting less than 1% of adult lung tumors. (15, 16)
Therapeutic options for patients with unresectable and/or advanced IMT are limited in particular for ALK negative cases. (17)
Other treatments besides surgery include radiation and chemotherapy.(18)
Dishop et al. reported a case treated with vincristine and etoposide as the first line and cisplatin, adriamycin, and methotrexate as the second line after incomplete resection. (19)
In addition, complete remission was reported using vincristine, ifosfamide, doxorubicin, and celecoxib (20)
Steroid and non-steroidal anti-inflammatory drugs have also been reported as effective for IMT. However the patient’s phenotype that can have a benefit for the treatment is stil debate. Steroids have been reported as effective for both IMT containing and IMT patients without IgG4SD features (21, 22)
On the other hand, Cerfolio et al. reported two cases where the remaining tumor showed no growth after incomplete resection during 4 to 9 years follow-up and the cases did not receive any additional treatment, although the biological features of those cases were not showed. (23)
ALK and / or ALK expression gene rearrangement has been described as a good prognostic marker in IMT, while ALK negative IMT appears to be more aggressive with a higher frequency of metastasis than ALK positive IMT (7, 3)
Among ALK rearrangements have been identified more than 10 different ALK fusion partner genes in IMT, including the most common TPM3/4, RANBP2, TFG, CARS, ATIC LMNA, PRKAR1a, CLTC, FN1, SEC 31A, and EML4 .Chromosomal translocation led to the formation of an ALK fusion protein which exhibits kinase activity independent of the ligand due to the self-phosphorylation of the chimeric protein. This results in prolonged survival of the cancer cell, hyperproliferation and enhanced cell migration. (24–29)
In contrast, actionable genomic alterations have not yet been described in about 50% of IMT samples that are negative for ALK by IHC. ALK-negative IMTs may be more aggressive than ALK-positive IMT with a higher frequency of metastasis. (3)
Our case showed a slowly growing ALK negative IMT in a AYA patient. Initially IMT was misdiagnosed and patients underwent radiological follow up for 4 years without any morphological modifications. After surgery the pathology report oriented for a salivary gland tumor of the lung and only after a second look the IMT was defined. This reflects the challenge in the diagnosis in case of ALK negative IMT.
Furthermore in case of ALK negative tumors little is known about their potential oncogenic drivers, so there are no targeted therapies available.
Recent studies have shown ALK-negative IMT might harbor other kinase fusions such as ROS1, NTRK, RET or PDGFR beta, which initiated genome-level research into potential tumorigenic drivers in ALK-negative subsets of IMTs.
In 2014 was published a study in which other possible IMT actionable targets were reported for the first time, involving ROS1 and PDGFR beta fusions. A genetic analysis was performed by NGS on 33 IMT samples, 11 of which were ALK negative specimens. In cases in which there was sufficient tumor material available, the kinase fusions were verified with RNA sequencing. Kinase fusion different from ALK fusion were identified in 6 of 11 ALK negative cases. Four contained distinct ROS1 fusions (sample L3/L4, YWHAE-ROS1, sample L6, TGF-ROS1) and 2 contained a PDGFR beta fusion (samples L7/L10, NAB2-PDGFR beta). They are both actionable targets of FDA-approved drugs. Notably, they also detected ALK fusions in 2 of 11 IMT samples that tested negative for ALK expression by IHC.(30)
ROS1 rearrangements are reported in approximately 9–13% of IMT, all ALK-negative cases (25, 31). Clinical cases of children/adolescents with pulmonary IMT with a TGF-ROS 1 rearrangement are present in literature. They all benefited from treatment with crizotinib (250 mg) with a significant reduction in tumor size. (31–34)
Jia He et al found for the first time a double amplification of CDK4 and MDM2 with protein overexpression by NGS and IHC in a 68-year- old woman with a gastric IMT with local invasion of spleen and diaphragm(35).
Furthermore, Antonescu et al. found correlations between the genotypes and certain clinic-pathologic characteristics of the IMT .(36) All cases have been tested for ALK gene rearrangements. ALK negative tumors have been further studied by FISH and RNA sequencing in some cases for abnormalities in ROS1, PDGFRB, NTRK1 and RET. About 6 ROS1 rearranged IMTs all except one is presented in children, mainly in the lung and intra-abdominal, with a specific growth of spindle cells with long cell processes. RET rearrangement was found in a 27-year-old pulmonary IMT characterized by a solid pseudosarcomatous growth and a fatal clinical outcome.
As reported above IMT has an increased incidence in children, adolescents and young adults (AYA). Our case was an asymptomatic young adult female of 18 yo. Initially due to the radiological characteristic of the nodule, the lacking of risk factors for neoplastic disease and the young age it was decided to follow radiologically the lung nodule and it was decided to perform the surgery only after a increasing in the size of the nodule. We would like to focus our attentntion onto the attitude into diagnostic and therapeutic strategies in cases of AYA should be different from that used in adult cases. Unfortunately there is a lacking of AYA specialized centers that should be implemented