1
Background
The incidence of bone metastases (BM) in advanced non-small-cell lung cancer (NSCLC)
patients is estimated to range from 30% to 40% [1], [2]. The presence of BM often
results in pathologic remodeling of the affected bone compartment, making affected
bones vulnerable to skeletal related events (SREs). SREs include pathologic fractures,
spinal cord compression, requirement for radiation, surgery to bone and hypercalcemia,
all reducing quality of life and worsening prognosis [3]. BM is a poor prognostic
survival factor [4]. Therefore, early diagnosis and adequate treatment of BM is critically
important issues of the clinical management of NSCLC patients.
To detect BM in NSCLC patients, bone scintigraphy combined with plain radiographs,
computerized tomography (CT) and magnetic resonance imaging (MRI) is recommended.
But routine radiography only gives definite diagnosis when the bone is already substantially
damaged by the tumor. Although scintigraphy is more sensitive, its specificity is
not satisfactory due to pseudo-positive values caused by inflammation and traumatic
fracture. Any abnormal scintigraphic findings should always be verified by radiographic
ones [5]. Bone scintigraphy is also a more expensive, invasive, time-consuming, and
exposes cancer patients to irradiation, limiting its use for monitoring purposes.
Since BM impairs the balance between bone formation and bone resorption, altered bone
remodeling activities can be assessed directly by measuring the components of affected
bone cells or indirectly by analyzing metabolic products released from the bone matrix
by changed rates of bone formation or resorption. Numerous new analytical tools for
bone turnover markers (BTMs) have improved the diagnosis of BM. These BTMs have been
recommended as helpful tools for assessing BM [6]. Collectively, there seem to be
a diversity of findings depending on cancer type and the type of BTMs used. Previous
researches had explored the applications of BTMs in NSCLC patients [7], [8], [9],
[10], [11], [12], [13], [14], [15], [16], [17], [18], [19], nevertheless, as to the
optimal markers and their proper application in BM screening, there hasn't been a
consistent agreement, which greatly hampered the BTMs usage in clinical practice.
Therefore, we (1) measured serum markers of bone formation and bone resorption as
noninvasive analytes of bone turnover in NSCLC patients with or without BM, (2) assessed
the diagnostic accuracy of these BTMs as potential indicators of BM in NSCLC patients,
combined diagnostic effectiveness of BTMs and (3) evaluated with univariate and multivariate
analysis of the usefulness of BTMs to make a prognosis in NSCLC patients with BM.
We selected bone-specific alkaline phosphatase (BALP), N-terminal midfragment of osteocalcin
(N-MID) and aminoterminal propeptide of type I collagen (PINP) as bone formation markers,
β-cross-linked carboxyterminal telopeptide of type I collagen (β-CTx) as bone resorption
markers.
2
Materials and methods
2.1
Patients and samples
2.1.1
Patients
Our retrospective study included 414 newly diagnosed NSCLC patients that were investigated
and treated in the department of internal oncology of the Sixth People's Hospital,
Shanghai Jiao Tong University between January 2010 and December 2013. All participants
signed approved written consents; the study was done in accordance with the Helsinki
Declaration II and Standards of Good Clinical Practice. The Local Ethical Committee
has approved the study protocol.
The study consisted of three groups: Group A included 193 NSCLC patients without BM
at diagnosis, Group B included 221 NSCLC patients with BM at diagnosis, and Group
control included 179 healthy volunteers. The diagnosis of all NSCLC patients was confirmed
by histological or cytological examination of specimens taken from bronchoscopy or
by CT-guided fine needle biopsy. Cancer stage was assigned according to the TNM system.
All patients underwent bone scanning using a radionuclide (Technetium-99m) scintigraphy
together with plain radiographs, CT and/or MRI to verify and quantify the presence
of BM. In special cases, affected bone lesions by CT-guided fine needle biopsy were
used to diagnose BM.
2.1.2
Patients' evaluation
Baseline evaluation included clinical assessment, bone survey, evaluation for extraskeletal
disease and serum BTMs determination.
Clinical evaluation included assessment of performance status according to the World
Health Organization (WHO) criteria. SREs at diagnosis were recorded, patients were
followed up for survival every 3 months and SREs in follow-up were also recorded.
Bone survey included bone scintigraphy and plain radiological, as well as CT or MRI
when necessary. Patients were initially classified according to the type and bulk
of BM, based on the findings of the bone survey. BM type was characterised as lytic,
blastic or mixed. The bulk of BM concerned the number of sites involved and was graded
as previously proposed by Soloway [20]. Briefly, Soloway 0 refers to patients without
BM; Soloway 1 refers to patients with <6 BM; Soloway 2 refers to patients with <20
BM; Soloway 3 refers to patients with >20 but less than a “super scan”; Soloway 4
refers to patients with “super scan” that is defined by a >75% involvement of the
ribs, vertebrae, and pelvic bones.
2.1.3
Samples
Blood samples were collected in plastic tubes between 07:30 and 09:00 a.m., stored
in ice and centrifuged at 2000g for 15 min, at 4 °C, within 2 h from venipuncture.
Blood samples were collected before the administration of any anticancer treatment
after initial diagnosis.
Bone Formation Markers. BALP was determined by the Tandem-MP Ostase Immunoenzymetric
Assay (Beckman Colter, Fullerton, CA), which specifically quantifies BALP with low
immunoreactivity for the liver/kidney isoforms [21]. N-MID (N-MID-Osteocalcin Assay,
Roche) and PINP (Total PINP-Assay, Roche) were measured on the Elecsys 2010 analyzer
(Roche). The PINP assay is a new electrochemiluminescent assay that detects both tri-
and monomeric PINP forms.
Bone Resorption Markers. β-CTX was determined by the β-CrossLaps Assay (Roche) on
the Elecsys 2010 analyzer [22].
2.2
Statistical analysis
Statistical calculations were performed with SPSS® 13 for Windows™ and GraphPad® Prism®
4.03. All results are expressed as mean±SD. We used the nonparametric Kruskal–Wallis
ANOVA with Dunn's post test, the Mann–Whitney U test, Spearman's rank correlation
coefficients and the Kolmogorov–Smirnov distribution fitting procedure. Diagnostic
accuracy was evaluated by Receiver-operating characteristic (ROC) curve analysis.
For the combined diagnostic effectiveness of BTMs, the probability was fitted by logistic
regression model and then analysed by ROC curves. The Kaplan–Meier product limit method
was used to determine survival probability in subgroups. Univariate and multivariate
analysis of risk factors predicting NSCLC specific death was performed using the Cox
proportional hazards regression model. Differences and associations were considered
statistically significant if p<0.05.
3
Results
3.1
Demographics characteristics
221 patients suffered from clinically manifest BM and 33.5% had more than seven BM
lesions. In group A, 1 or more metastases in the lung, liver, and other sites (excluding
brain) were present in 49.1% patients, while in group B the number is 44.6%. The majority
of the patients in both groups received chemotherapy during the study (55.4% in the
group A and 80.5% in the group B), and 22.8% in the group A and 29.0% in the group
B received target therapy. There were no age or sex difference among the subgroups.
For further clinicopathologic data see Table 1, Table 2.
3.2
Serum BTMs in the study groups
Fig. 1 shows the scatter plots and medians of all BTMs among the subgroups. Since
all markers showed a Gaussian distribution using the Kolmogorov–Smirnov test, we calculated
the parametric upper 95% reference limits. Briefly, ANOVA analysis showed bone formation
BALP, PINP, N-MID and bone resorption β-CTx values were higher in BM patients than
in the control group (p<0.05) and in patients without BM (p<0.05), but no difference
was found between the control group and the group without BM (p>0.05). For further
data see Fig. 1.
3.3
BTMs as diagnostic Indicators of BM
3.3.1
ROC analyses between NSCLC patients with or without BM
ROC analyses were performed to characterize the diagnostic usefulness of the BTMs,
which is to differentiate NSCLC patients with or without BM (Fig. 2 and Table 3).
Both bone formation and resorption markers were helpful in this respect. ROC curves
were drawn according to the markers based on true-postive ratio (patients with BM)
and false-positive ratio (patients without BM). It was obvious that all BTMs were
rather effective for this purpose of differentiation. BALP was the most sensitive
marker (Area under curve(AUC): 0.787±0.056). Sensitivity and specificity were calculated
using cut-off values that correspond to the 95% specificity of the marker tests in
the group of NSCLC patients without BM. The cut-off values were found to be 16.96 μg/L
for BALP, 52.75 ng/mL for PINP, 12.65 ng/mL for N-MID and 507 ng/L for β-CTx.
3.3.2
ROC curves analysis of the combination of BTMs
When BTMs were combined for BM screening (Fig. 3 and Table 4), the AUC was elevated.
The most effective combination was PINP and β-CTx, to 0.833 (95% CI, 0.785 to 0.882,
p<0.0001), and the optimal probability indicated an optimal cut-off value as PINP
40.5 ng/mL and β-CTx 584 ng/L (sensitivity: 61.0%, specificity: 91.2%).
3.4
Association between BTMs and clinical outcome
Table 5 shows associations between clinical outcome and all BTMs. The demographic
data for patients stratified according to Soloway score is indicated in Table 2. There
were no linear associations between Soloway score and the demographic characteristics
of patients. All BTMs indicated that linear increases with advancing severity of the
metastatic involvement of the skeletal system. BALP, PINP and β-CTx were significantly
higher in patients with multiple bone site involvement (Soloway 2/3 and 4) than those
with few bone site involvement (Soloway 1) (*p<0.05).
No BTMs have any significant difference among patients with lytic, blastic or mixed
bone lesions (p>0.05). Neither bone formation markers nor bone resorption markers
differed significantly between patients with bone plus visceral metastases and those
with bone metastases only (p>0.05). When patients with BM only or patients with bone
and visceral metastases and patients with only visceral metastases were compared with
those don't exhibiting metastases, BTM were significantly higher in the two groups
with BM with or without visceral metastases (p<0.05). For further data see Fig. 4.
During the study period, SREs occurred in 84 out of 221 patients (38.0%). 61 patients
(27.6%) required bone radiation, 27 patients (12.2%) received surgery to bone, 23
patients (10.4%) with pathologic fractures, 8 patients (3.6%) with spinal cord compression
and 6 patients (2.7%) with hypercalcemia. Patients with SREs in follow-up had higher
β-CTx, BALP or PINP levels compared with patients without SREs (p<0.05), while levels
did not differ significantly between patients with or without SREs at diagnosis (p>0.05).
3.5
BTMs as predictors of survival
202 of 221 patients were eligible for survival analyses. Median followup was 15 months
(range 4 to 40). The primary end point of the analyses was NSCLC related survival.
A total of 170 patients died from NSCLC. To determine whether serum BTMs correlate
with disease outcome, patients were stratified into 2 groups by analyte cutoff points
using the 95th percentiles. To identify the significant prognostic factors associated
with NSCLC specific death, univariate and multivariate risk factor analyses were performed
using the Cox proportional hazards regression model in the stratified groups (Table
6). BALP, ECOG, Visceral metastases and SREs were significant univariate predictors
of death from NSCLC. These results corresponded to Kaplan–Meier survival analysis
curves. Patients with BALP above the 95% cutoff, worse ECOG, visceral metastases or
SREs had significant shorter survival time than patients with a lower BALP concentration,
better ECOG, only bone metastases or without SREs. However, multivariate analysis
of the significant predictors showed that BALP, ECOG and SREs were independent predictors
of NSCLC related death (Table 6). The median survival time of the patients with normal
BALP was 18.0 months, significantly longer than 13.8 months in the patients with elevated
BALP (95%CI 12.5–15.1, p<0.05) (Fig. 5). They remained significant variables in the
forward and backward stepwise calculation models.
4
Discussion
Previous reports evaluating BTMs for the detection of BM in patients with malignant
diseases have concluded that urinary N-telopeptide of type I collagen (NTx) is the
most useful BTMs [6], [11], [23]. The usefulness of uNTx to diagnose early BM has
been reported in several studies [24], [25], [26]. Analyses were performed in both
serum and urine, but consistent results were not always described. The pre-analytic
variability of BTMs, their different stability in vitro especially in urine and use
of assays with different antibodies recognizing different epitopes may explain many
of the discrepant results [28], [29], [30], [31]. Seibel [32] indicated serum as the
preferred matrix for measurement. He reported the need to measure formation markers
(BAP, N-MID, PINP) in serum. Among resorption markers, collagen-derived products can
be measured in serum and urine (β-CTx, NTx).
In our opinion, the preferred sample matrix is serum. The use of a single serum for
the measure of multiple markers is desirable to simplify pre-analytical and analytical
procedures. As commercial assays for measuring BTMs in serum are available, we evaluated
the diagnostic value of BTMs in clinical use in detecting BM in NSCLC patients, BALP,
PINP and OC, bone formation markers, and CTX, bone resorption markers, which can all
be measured in automatically in on sample are assessed. To avoid these discrepancies
as far as possible, we measured BTMs exclusively in serum collected during a defined
time period, between 7:00 and 9:00 A.M.
The diagnosis of BM in NSCLC patients relies predominantly on imaging techniques.
Although these techniques provide useful diagnostic tools, their use for early diagnosis
or close monitoring of patients is not without limitations. BTMs as indicators for
BM in NSCLC patients have been studied, but there are no clear recommendations which
markers or marker combinations should be used [7], [8], [9], [10], [11], [12], [13],
[14], [15], [16], [17], [18], [19]. Kong [22] found that the increased CTX level had
the specificity and sensitivity of 65.6% and 68.8%, respectively, in the diagnosis
of BM in NSCLC patients, and they speculated that CTX could be used to screen the
BM of NSCLC. Ebert [7] found the concentrations of the bone markers BALP, PINP were
significantly higher in patients with BM than in those without BM.
In our attempt to document the predictive value of these BTMs in NSCLC patients, we
studied a cohort of 414 cancer patients with or without radiographic evidence of BM.
We measured the levels of several BTMs in NSCLC patients to assess which BTMs, if
any, best reflected the presence of BM. Compared with previous literatures [12], [13],
[15], [16], [34], we chose NSCLC patients with no evidence of BM as the control group
instead of healthy people. It is known that the balance of bone metabolism is regulated
through the action of various systemic hormones and local mediators. We assumed that
the formation of tumor in the body, even without evidence of BM, may influence the
concentration of those hormones and mediators and result in up-regulation of BTMs.
Our results showed the levels of BALP, PINP, N-MID, and β-CTX in the BM group were
significantly higher than those in without BM groups. The sample size is considerable
and the study provides a valid confirmation of previous reports in smaller studies.
In addition to the clinical validity, both assays were uncomplicated and reliable
with good analytic performance; thus, they fulfilled the essential preconditions for
routine measurements. The PINP, N-MID and β-CTx assay was an automated assay on a
general-purpose analyzer (Elecsys). Meanwhile, BALP could also be automated measured
on an analyzer (Access, Beckman–Colter).
Although our work has demonstrated that serum BTMs work well in BM screening, we preferred
not to define them as methods for BM diagnosis, nor did we consider that they could
replace the screening function of imaging methods. This is because BM is a complicated
process, and serum BTMs of an individual patient may be influenced by unknown elements.
Serum markers are also unable to fulfill some functions of imaging methods, such as
localizing the bone metabolic abnormality.
In our study, the levels of BALP, PINP and β-CTx in the serum were significantly (p<0.05)
correlated with the number of skeletal sites involved with metastases, but there was
no significant difference in the levels of BTMs among patients with olytic lesions,
blastic lesions and mixed lesions. A possible explanation to these findings could
be that tumors may secrete these bone regulatory proteins regardless of their location,
thus circulating levels maybe elevated even when skeletal involvement has not emerged.
Histomorphological results show that osteolytic and osteoblastic metastases are characterized
by simultaneous resorptive and osteoblastic processes [6]. The simultaneous increases
of bone formation markers and bone absorption markers indicate that the bone formation
and bone absorption occur at the same time in patients with BM.
One feature of our research was that we chose two BTMs and combined them for analysis.
As the univariate evaluation of data showed dissociated changes of serum marker concentrations
for both bone formation and resorptions, multivariate analysis was appropriate. Logistic
regression analysis of all variables showed that the combination of β-CTx and PINP
was the best way to differentiate between BM and nonmetastases. We assumed that simultaneous
elevation of the two BTMs could represent a more robust judgement for BM. Our data
was consistent with this assumption: when the bone formation markers and bone resorption
markers were used together, the sensitivity and specificity for BM screening were
improved as compared with the BTMs being used separately.
Another feature of our research was that we used BTMs clinically to predict the risk
of SREs. We found that if patients had a higher β-CTx, BALP or PINP levels at baseline,
they were at a higer risk of SREs. A similar pattern was seen in an study [3] evaluating
NTx and BALP levels for 441 patients on the placebo arms of the previously noted clinical
trials of zoledronic acid in patients with BM from prostate cancer, NSCLC and other
solid tumors. Patients with high NTx or BALP levels had a greater incidence of SREs
compared with patients with low levels of NTx or BALP. Because survival after diagnosis
of BM is relatively short for patients with NSCLC, methods are needed to predict SREs
in a shorter timescale than it is possible with current imaging methods. From the
results of our current study, the use of BTMs at baseline may make a major contribution
to this need by identifying those patients at highest risk who warrant the highest
priority for intervention to prevent SREs.
In our study, we evaluated the relationship between serum BTM levels and overall survival
(OS) in NSCLC. Correlation analysis revealed that BALP was related to the survival
time. Regression analysis showed the number of BM sites, the characteristics of BM
(lytic, blastic or mixed), sex and Soloway score did not significantly affect the
survival time. When considering the 4 markers that we studied, BALP was the only significant
univariate predictor of death from NSCLC. Patients with low serum BALP tend to have
longer survival than those with high BALP. The prognostic significance of BALP was
verified by multivariate Cox regression analysis since BALP, ECOG and SREs were independent
factors of cancer related death. Thus, BALP really appeared to be more a marker of
tumor burden or activity than a simple indicator of bone turnover. In addition, the
association of BALP with the survival of NSCLC patients could be used for stratifying
patients with advanced NSCLC for clinical trials in the current treatment options
with bisphosphonates or other chemotherapeutic agents to individualize treatment.
For patients with NSCLC, although this analysis cannot address the possibility of
a causal link between increases in BTMs and OS, it does suggest that higher BTMs at
baseline could have a negative effect on disease progression and might worsen survival.
Some studies assessing the relationship between urinary NTx level and OS in NSCLC
have shown that high urinary NTx levels are associated with an increased risk of death
[26], [35], [36]. Further, recent studies have suggested that zoledronic acid and
denosumab reduce baseline urinary NTx level [25], [36]. Moreover, patients with NSCLC
and high baseline NTx levels that were normalized after chemotherapy including zoledronic
acid were found to experience longer survival compared with patients whose NTx levels
remained persistently high [6], [36], [37]. These study inspired us to find the relation
between the change of BTMs and OS. The results of a randomized prospective study would
be more credible, and that is what we want to do in the future. But our finding that
baseline BTMs levels were predictive of death is also important because it can be
argued that baseline BTMs assessments allow more time for appropriate intervention.
5
Conclusion
Our results suggest that, despite of the limitations, measurement of serum BTMs concentration
is a powerful test alone or in combination with other BTMs to detect BM and to predict
SREs and survival probability in NSCLC patients. However, to fully establish the role
of BTMs in clinical practice, prospective studies are needed. Now our suggestion for
the proper application of serum BTMs in BM screening is as follows: serum BTMs should
be evaluated at once since a patient is diagnosed NSCLC to establish his/her baseline
values, and then be monitored regularly and compared with his/her previous results.
If the baseline values are higher than the cut-off value, or if abnormal variation
is found during the follow up, imaging methods should be applied for further confirmation.
If necessary, appropriate intervention should be taken as soon as possible. If the
serum BTMs would be used this way, BM screening could become more timely and accurate.
As a result, meaningful improvements of life quality and treatment to NSCLC patients
may be achieved.
Conflict of interest
None of the authors have identified a conflict of interest.