Efficacy and safety of low-dose Sirolimus in Lymphangioleiomyomatosis

The present study included 39 patients with LAM (82.1% biopsy-proven cases) treated with sirolimus between May 2011 and March 2016 at Asan Medical Center, Seoul, Republic of Korea (Fig. 1). All subjects met the diagnostic criteria of the American Thoracic Society/Japanese Respiratory Society guideline [14]. Subjects treated with sirolimus, who had mean blood trough levels maintained < 5 ng/mL, were classified as the low-dose sirolimus group. Informed consent was waived, and the study was approved by the Asan Medical Center Institutional Review Board (2016–0480).

Clinical and survival data for all patients were retrospectively obtained from medical records, telephone interviews and/or National Health Insurance records. All subjects were routinely follow-up at 3-month intervals, and pulmonary function tests and measurement of blood sirolimus levels were performed at each follow-up visit. Whole blood sirolimus levels were measured by liquid chromatography-tandem mass spectrometry (LC-MS). Spirometry and measurement of the diffusing capacity of the lung for carbon monoxide (DLco) were performed according to the recommendations of the American Thoracic Society (ATS) and European Respiratory Society, and the results were expressed as percentages of normal predicted values [15‐17]. The six-minute walk test was performed according to ATS guidelines [18].

Efficacy was evaluated in patients who were treated with sirolimus for more than 12 weeks and who underwent pulmonary function tests more than three times before and after treatment (Fig. 1). Changes in lung function, specifically, forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and DLco, from baseline to 12 or 24 months before and after treatment were evaluated. The rate of decline in lung function was estimated by linear regression modelling and compared before and after treatment. For categorical comparison, disease progression was defined as any decline in FEV₁ during the observation period. The treatment response of extra-pulmonary manifestations was assessed in patients with AML or lymphangioma who had follow-up CT images using the Response Evaluation Criteria in Solid Tumours (RECIST) criteria (version 1.1) [19] and classified as follows: complete response (completely disappeared tumor), partial response (≥ 30% decrease in the sum of longest diameters of target lesions), progression (≥ 20% increase in the sum of longest diameters), and stability (all other changes). In this study, complete or partial responses were regarded as ‘improvement’.

Safety was evaluated in all patients who received at least one dose of sirolimus (Fig. 1). AEs were identified from the initiation of treatment to 28 days after the last dose and were classified using the preferred terms in the Common Terminology Criteria for Adverse Events (Version 4.0). SAEs were defined as any AEs occurring with any dose that resulted in any of the following outcomes: death, hospitalisation for life-threatening causes, disability or permanent damage, intervention to prevent permanent impairment or damage, or other serious medical events.

All values are reported as mean ± standard deviation (SD) for continuous variables or as percentages for categorical variables. Student’s t-test and the Mann–Whitney U test were used for continuous data, and Pearson’s chi-square test and Fisher’s exact test were used for categorical data. Comparison of the rate of lung function decline and changes in lung function before and after treatment were performed by unpaired t-tests with or without Welch’s correction, as appropriate. All statistical analyses were performed using IBM SPSS, Version 21.0 (IBM Corp., Armonk, NY, USA). A two-tailed p-value < 0.05 was considered to indicate statistical significance.

Of the total of 39 patients, 51% were classified as receiving low-dose treatment. The median treatment period was 29.6 months (29.2 months in the low-dose group vs. 30.0 months in the conventional-dose group, p = 0.261), and mean blood sirolimus level was 5.5 ± 2.8 ng/ml (3.5 ± 1.3 ng/ml in the low-dose group vs. 7.7 ± 2.3 ng/ml in the conventional-dose group, p < 0.001). In the low-dose group, the mean trough level of sirolimus was maintained below 5 ng/ml during the treatment period (Additional file 1: Figure S1). There were no differences between the low- and conventional-dose groups in age, gender, smoking history, prior treatment, extrapulmonary manifestations, lung function or exercise capacity (Table 1). However, more subjects in the low-dose group had TSC (30.0% vs. 0.0%, p = 0.020). Most subjects in the low-dose group maintained low blood trough levels due to adverse events (AEs, 67.5%) or a stable disease course after initial treatment (25.0%) (Additional file 2: Table S1). Among patients with TSC-LAM (n = 6), four received low-dose sirolimus due to azotaemia (n = 1) and treatment history of the renal procedure due to AML (n = 3) and remaining two did due to mucositis.

In the whole group, changes in FEV₁ significantly improved 12 and 24 months after treatment (∆FEV₁, 3.4 ± 9.3% predicted at 12 months, p = 0.004; 6.9 ± 11.5% predicted at 24 months, p = 0.007) compared with those before treatment (∆FEV₁, − 4.2 ± 8.2% predicted; Fig. 2a). The changes in DLco also exhibited similar trends after treatment (∆DLco, 3.1 ± 7.7% predicted at 12 months, p = 0.006; 2.4 ± 8.0% predicted at 24 months, p = 0.032; Fig. 2b). By contrast, FVC only showed a numerical improvement after treatment (∆FVC_, 3.1 ± 7.7% predicted at 12 months, p = 0.250; 6.8 ± 14.8% predicted at 24 months, p = 0.582; Fig. 2c).

In the low-dose group, FEV₁ showed an improving trend at 12 and 24 months after treatment (∆FEV₁, 4.2 ± 11.6% predicted at 12 months, p = 0.169; 7.2 ± 12.0% predicted at 24 months, p = 0.212) without statistical significance (Fig. 2a). DLco (∆DLco, 6.6 ± 14.0% predicted at 12 months, p = 0.145; 6.6 ± 14.0% predicted at 24 months, p = 0.250) and FVC (∆FVC_, 3.4 ± 10.7% predicted at 12 months, p = 0.283; 2.7 ± 11.1% predicted at 24 months, p = 0.891) also showed similar trends (Fig. 2b and c). On the other hands, the conventional-dose group showed significant improvements in FEV₁ (∆FEV_1, 2.7 ± 7.0% predicted at 12 months, p = 0.010; 6.6 ± 11.7% predicted at 24 months, p = 0.015; Fig. 2a) and DLco (∆DLco_, 2.8 ± 3.7% predicted at 12 months, p = 0.001; 2.1 ± 2.6% predicted at 24 months, p = 0.010; Fig. 2b) at 12 and 24 months after treatment; however, only numerical improvements in FVC were observed after treatment (∆FVC, 2.2 ± 5.9% predicted at 12 months, p = 0.608; 6.9 ± 6.5% predicted at 24 months, p = 0.233; Fig. 2c). There were no differences between the two groups in changes in lung function (FEV₁, FVC and DLco) before and after treatment.

In the whole group, the rate of decline in FEV₁ was significantly reduced after treatment (− 0.12 ± 0.47% predicted/month [before] vs. 0.24 ± 0.48% predicted/month [after], p = 0.027) compared with before treatment (Additional file 3: Table S2). The rate of decline in DLco (− 0.33 ± 0.61% predicted/month [before] vs. 0.03 ± 0.26% predicted/month [after], p = 0.006) was also reduced after treatment, but that of FVC was not.

In the low-dose group, the rate of decline in FEV₁ showed an improving trend after treatment (− 0.08 ± 0.38% predicted/month [before] vs. 0.19 ± 0.51% predicted/month [after], p = 0.264) without statistical significance (Additional file 3: Table S2). There were similar trends in the rates of decline in FVC and DLco after treatment. However, in the conventional-dose group, the rates of decline in FEV₁ (− 0.26 ± 0.54% predicted/month vs. 0.22 ± 0.38% predicted/month, p = 0.024) and DLco (− 0.55 ± 0.58% predicted/month vs. 0.04 ± 0.25% predicted/month, p = 0.002) were significantly reduced after treatment (Additional file 3: Table S2).

In the whole group, the rate of disease progression, which was defined as any decline in FEV₁, decreased after treatment (77% before vs. 33% at 12 months [p = 0.008] vs. 35% at 24 months [p = 0.024]) (Fig. 3a). In the low-dose group, the rate of disease progression showed a trend towards decrease after treatment (63% before vs. 43% at 12 months [p = 0.659] vs. 44% at 24 months [p = 0.637]) (Fig. 3b). In the conventional-dose group, however, the rate of disease progression decreased significantly after treatment (100% before vs. 25% at 12 months [p = 0.006] vs. 25% at 24 months [p = 0.021]) (Fig. 3c).

Among 18 patients with extra-pulmonary manifestations, 11 (61.1%) were assessed for treatment responses. The median observation time from the initiation of sirolimus to the last CT follow-up during treatment was 2.9 years (range: 1.4–5.8 years; 2.8 [low] vs. 3.1 [conventional] years, p = 0.631). In the whole group, five (45.5%) patients showed improvement and 6 (54.5%) showed stability. Comparison of the results between the low and conventional groups were similar; in the low-dose group, improvement and stability were observed in 2 (28.6%) and 5 patients (71.4%), respectively and in the conventional-dose group, those were observed in 3 (75.0%) and 1 patients (16.7%), respectively (p = 0.242).

Of all patients, 89.7% experienced AEs, averaging 3.46 AEs per patient (Table 2 and Additional file 4: Table S3). The most common AE was hypercholesterolaemia (43.6%), followed by stomatitis (35.9%). The rate of AEs in the low-dose group did not differ from that in the conventional-dose group (85.0% vs. 94.7%, p = 0.605). Although there were no significant differences in AEs between the groups, the most common AE in the low-dose group was stomatitis (50.0%), whereas hypercholesterolaemia was the most common in the conventional-dose group (52.6%). The rate of AEs per patient was also comparable in the two groups (3.70 events per patient in the low-dose group and 3.21 events per patient in the conventional-dose group, p = 0.406) (Additional file 4: Table S3).

Serious adverse events (SAEs) occurred in 17.9% of all subjects, and there was no significant difference in the rate of SAEs between the low- and conventional-dose groups (15.0% vs. 21.0%, p = 0.695) (Table 2). Although there were no significant differences in the rate of AEs between the groups, the most common SAEs were infection (15.0%) in the low-dose group and pneumothorax (10.5%) in the conventional-dose group. There were no deaths during follow-up.

Seven patients (17.9%) permanently discontinued treatment due to planned pregnancy (7.7%), AEs (5.1%), or stable disease status (1.1%). Although the overall discontinuation rate was lower in the low dose group (5.0% [low] vs. 31.6% [conventional], p = 0.044) than in the conventional dose group, the discontinuation rate due to AEs were not different between two groups (5.0% vs. 5.3%, p = 1.000; Additional file 5: Table S4). Of the two patients who discontinued sirolimus due to AEs, one in the low-dose group discontinued because of stomatitis and one in the conventional-dose group discontinued due to stomatitis and urticaria.