Radiological osteosclerotic change by gefitinib
EGFR-TKIs significantly extend progression free survival and median OS in patients with NSCLC harboring EGFR-TKIs sensitizing mutation. However, few original studies have assessed their clinical effect for skeletal metastasis. This study is the first report to investigate the radiological effect for bone metastasis in patients with NSCLC harboring EGFR-TKIs sensitizing mutation treated with gefitinib.
The present study revealed that as much as 98% of the bone metastases in patients with NSCLC harboring EGFR mutation after treatment with gefitinib responded to show osteosclerotic change, and 51% of patients achieved CR. In 2012, Yamashita et al. reported that 11 out of 41 NSCLC patients treated with gefitinib, demonstrated osteosclerotic changes [16]. Their report had excluded patients who underwent RT, other anti-cancer drugs, or bone-modifying agents but crucially, had not accounted for the presence of EGFR mutations. The osteosclerotic rate in Yamashita’s report was 27%, lower than the 98% observed in the current study. The discrepancy may well be attributable to the GEF group in the current study including only patients with EGFR mutation and not excluding patients who underwent local RT or bone-modifying agents. Approximately 30% of the patients with lung adenocarcinoma in Eastern Asia are EGFR mutation positive [17]. Assuming that 30% of the 41 subjects in the report by Yamashita et al. had been patients harboring EGFR-TKIs sensitizing mutation, the 11 cases (27%) of osteosclerotic change could have occurred mostly in patients harboring EGFR mutation.
The effect of conventional chemotherapy with cytotoxic drugs on bone metastases is unclear. Sun et al. reported that the skeletal-related events occurrence rate by conventional cytotoxic chemotherapy was as high as 59 out of 81 (73%). However, this significantly decreased after EGFR-TKI treatment [18]. The current study compared patients treated with gefitinib without RT and control patients without RT. CR and PR rates were 94% in the GEF w/o RT group but 27% in the control w/o RT group. These results suggest that the osteosclerotic response is expected in 27% of cases treated with cytotoxic chemotherapy alone. Whereas, for patients harboring EGFR mutation, EGFR-TKI alone can achieve response as osteosclerotic changes even without RT for lung-cancer derived bone metastases.
Effects of adding RT for patients who are candidates for gefitinib
In 2010, Harada et al. reported that 42% of the patients with bone metastasis responded to RT and 10% showed CR by their criteria [14]. As we mentioned before, the current study demonstrated that radiological response in bone metastases from patients with NSCLC harboring EGFR-TKIs sensitizing mutation to gefitinib treatment without RT was PR or better in 94% and CR in 31% of cases. This result raises the question as to whether or not RT is necessary. According to our study, the GEF with RT group showed significantly better local response maintenance rate at 1 year than the GEF w/o RT group. The interval to show response on images also tended to be shorter in the GEF with RT group. These results indicate that combining RT with gefitinib treatment is effective to maintain local control, and that it may contribute to earlier response.
Regarding progression-free survival of first-generation EGFR-TKIs for patients harboring EGFR mutation, it was reported to be between 9.2 and 12 months [19]; however, there are no reports about how long the sclerotic response of bone metastases continues. As shown in Fig. 6, without RT (GEF w/o RT group), the local response maintenance rate declines sharply around 300 days from the start of gefitinib therapy. Consequently, the local response maintenance rate of the GEF w/o RT group becomes similarly low to that of the control w/o RT group. This means that the sclerotic response in bone metastasis induced by gefitinib lasted for a similar period as that in the primary lesion or its visceral metastasis.
Mechanism of osteosclerotic change by gefitinib
Normanno et al. found that gefitinib inhibited induction of osteoclast differentiation through reduction in receptor activator of nuclear factor kappa-B ligand (RANKL) expression [20]. It has been reported that EGFR mutation is involved in the RANKL pathway [21, 22] and EGF signals are involved in bone metastasis of many cancers [23, 24].
Kishimoto et al. reported an NSCLC case in which bone metastasis showed a remarkable osteosclerotic change after multimodal therapy including gefitinib [25]. Pathological specimens of the bone lesion collected at autopsy revealed trabeculae composed of cartilage matrix, woven bone, and osteoids surrounded by osteoblasts, findings associated with ossification, suggesting repair after microfracture due to weakening by the osteolytic tumor. These studies suggest that gefitinib may act in a suppressive manner to osteoclasts and promote osteosclerotic change of bone metastasis.
Currently, third-generation EGFR-TKIs are widely used. In the FLAURA trial conducted in 2017 [26], gefitinib (first generation) and osimertinib (third generation) were compared. The study demonstrated that PFS with osimertinib was 18.9 months, significantly longer than that with gefitinib (10.2 months). However, there was no significant difference in the response rate between them. In this study, we investigated patients treated with first-generation EGFR TKIs and demonstrated that the median local response maintenance rate in the GEF w/o RT group was 11.7 months, which is similar to the results of the gefitinib in FLAURA trial. Therefore, considering third-generation EGFR-TKIs were associated with a longer PFS than first-generation EGFR-TKIs in the FLAURA trial, a longer duration of response after treatment with third-generation EGFR-TKIs for bone metastases may be expected.
The present study is of course subject to limitations. First, most of the patients were diagnosed with bone metastasis based on radiological images and did not have pathological evidence. However, patients with double cancers or conditions atypical for lung cancer were excluded from this study. In addition, CT or PET-CT images were compatible with typical bone metastasis findings. Therefore, we believe that the diagnosis was correct. If there are multiple bone lesions that show typical features of bone metastasis radiographically in advanced lung cancer, then it would be reasonable and beneficial for a patient to start treatment for lung cancer with bone metastasis without performing bone biopsy.
Second, we only enrolled symptomatic patients with bone metastases who could be followed up for three months or more and who could be regularly followed up with imaging study; therefore, there can be a bias that drop-outs or patients who died within three months as well as those who opted for best supportive care were not enrolled in this study. Asymptomatic patients with bone metastases were not included in the study, partly because of the lack of frequent imaging evaluation. A prospective randomized study enrolling more patients would be necessary to establish the effect of EGFR-TKI treatment on bone metastasis conclusively.
Third, we could not exclude the effect of bone-modifying agents. Quattrocchi et al. analyzed 23 patients with bone metastasis including six cases of lung cancer and reported that an increase of at least 50% bone density was observed in 87% of patients after three months of zoledronic acid therapy [27]. Therefore, osteosclerotic effect in the gefitinib group may partly be enhanced by bone-modifying agents. In the current study, 56% of patients in the gefitinib group and 47% of them in the control group regularly received zoledronate.
In conclusion, our study revealed that gefitinib treatment for patients with NSCLC harboring EGFR-TKIs sensitizing mutation causes osteosclerotic changes of lytic or mixed bone metastasis in 98% of patients. Moreover, the effect of gefitinib could continue up to a median duration of 270 days, which is similar to the progression-free period of gefitinib for internal organs reported in literature. Radiotherapy for bone metastasis is effective in maintaining the osteosclerotic effect of gefitinib.