1. Introduction
Lung cancer is one of the most common malignant tumors, with persistently high incidence and mortality rates. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancer cases, with a five-year survival rate of about 17.1%.
[1] NSCLC frequently metastasizes to bones, brain, other lung regions and liver, with bone metastasis accounting for approximately 30%-40% of all lung cancer metastasis.
[2] Pathological fractures caused by lung cancer bone metastasis, whether impending or actual, represent a difficult and challenging complication that impacts the prognosis of lung cancer patients, diminishes their quality of life, and may even be life-threatening.
[3] Clinically, the diagnostic methods for lung cancer bone metastasis recommended by guidelines primarily rely on imaging examination results. According to relevant statistics, approximately 70% of patients with lung cancer are often diagnosed at the intermediate or advanced stages of bone metastasis, having already lost the opportunity for curative lung cancer surgery.
[4] Currently, there are few clinically effective methods for predicting bone metastasis in lung cancer. Studies indicate that various types of molecules, host cells, and the extracellular microenvironment participate in the interactions of cancer cells during lung cancer bone metastasis, including osteoclast-mediated bone resorption and osteoblast-mediated bone formation.
[5] Therefore, we speculate that biochemical bone metastasis likely occurs prior to imaging bone metastasis. To further enhance the prediction, diagnosis, and disease monitoring of lung cancer bone metastasis, this study aims to conduct a combined analysis of SPECT/CT maximum standardized uptake value (SUVmax) with existing biochemical markers of bone metabolism: serum alkaline phosphatase (ALP), molecular fragments in the N end of osteocalcin (N-MID) and bone mineral density (BMD). This integrated approach seeks to provide a robust theoretical foundation for clinical prediction, diagnosis, and treatment monitoring of bone metastasis.
2. Data and methods
2.1 General information
A total of 107 patients diagnosed with lung cancer at a tertiary-level Class A hospital between January 2021 and June 2022 were enrolled. The cohort comprised 63 males and 44 females. Forty-eight patients were aged < 60 years, while 59 patients were aged ≥ 60 years. Among them, 37 patients had bone metastasis from lung cancer, and 70 patients did not have bone metastasis.
Inclusion criteria are listed as follows: (1) Pathologically or cytologically confirmed lung cancer: characterized by irregular cell morphology, small nuclei, etc.; bone metastasis demonstrated by imaging studies
[6] showing multiple patchy or cotton-ball-like lesions, diffuse high-density shadows with indistinct borders; (2) Karnofsky Performance Status (KPS) ≥ 70 points;
[7] (3) No prior radiotherapy or chemotherapy before enrollment; (4) Informed consent obtained from both the patients and family members.
Exclusion criteria are listed as follows: (1) History of osteoarthritis, rheumatoid arthritis, or other bone metabolic disorders; (2) Use of medications affecting bone metabolism (e.g., corticosteroids, bisphosphonates) within the past 6 months; (3) Traumatic fracture within the past year; (4) Individuals with psychiatric disorders or communication impairments.
2.2 Experimental methods
2 mL of fasting blood from each patient were collected in the morning, and then centrifuged at 2,000 rpm for 10 minutes at low temperature, and the collected serum were immediately stored at -80℃ in the refrigerator, ALP levels were measured by use of Olympus AU5400 automated biochemical analyzer, serum N-MID and total procollagen type 1 N-terminal propeptide (TPINP) levels were detected by an automated chemiluminescent immunoassay analyzer.
Bone Density Testing: Bone density (g/cm2) was measured by using dual-energy X-ray absorptiometry (DXA) at the first to fourth lumbar vertebrae, both femoral necks, and the entire hip joint. BMD refers to the bone mineral content per unit area in g/cm2, with the precise value expressed to three decimal places. The testing instrument was Lunar DXA bone densitometer manufactured by GE Healthcare, recognized by World Health Organization (WHO) as the gold standard for diagnosing BMD and osteoporosis.
2.3 SPECT/CT examinations
The new GE Infinia VC Hawkeye PET/CT system, featuring a low-energy high-resolution collimator, was employed in this study. The radiotracer 99mTc-MDP was supplied by the China Institute of Atomic Energy, with a radiochemical purity of > 95%. The patient received an intravenous injection of 25 mCi of 99mTc-labeled methylene diphosphonate (MDP). After drinking 500 mL of water, the patient was instructed to empty the bladder 3-4 hours later. The patient was positioned supine for anterior and posterior whole-body bone scintigraphy. The matrix was 256 × 1,024, the energy peak was 140 keV, and the window width was 20%. Analgesics were administered to patients experiencing severe pain, and local static bone scintigraphy were conducted when necessary.
2.4 Statistical treatment
SPSS 20.0 statistical software was applied to the statistical analysis. The measurement data included SUVmax, ALP, N-MID and TPINP, etc., presented as (
![]()
s). Independent sample
t-tests were used to analyze the differences between two groups, while the analysis of variance (ANOVA) was used to assess the differences among multiple groups. Categorical data, including gender, were expressed as n (%). Differences between groups were analyzed using chi-square (
χ2) tests. Diagnostic value was assessed using receiver operating characteristic (ROC) curve analysis. Inter-group comparisons with
p < .05 were considered statistically significant.
3. Results
3.1 Comparison of clinical data between lung cancer patients with and without bone metastasis
Patients with lung cancer bone metastasis exhibited significantly higher levels of ALP, N-MID, and TPINP in comparison to those without bone metastasis (
p < .05), while their lumbar spine BMD was significantly lower than that in patients without bone metastasis (
p < .05). No statistically significant differences were observed between bone metastasis and non-metastatic patients in terms of gender, pathological type, or other characteristics (
p > .05) (see
Tables 1-
4).
3.2 Relationship between SUVmax and clinical pathological characteristics in patients
Patients with adenocarcinoma exhibited significantly lower SUVmax values in comparison to those with squamous cell carcinoma and other types (
p < .05). Patients with tumors > 5 cm in diameter and TNM stage III–IV demonstrated significantly higher SUVmax values than those with tumors ≤ 5 cm in diameter and TNM stage I–II (
p < .05) (see
Tables 5-
9).
3.3 Relationship of ALP, N-MID and TPINP with clinical-pathological characteristics in patients
Patients with TNM stage III–IV showed significantly higher levels of ALP, N-MID and TPINP in comparison to those with TNM stage I–II (
p < .05). There were no statistically significant differences in ALP, N-MID and TPINP among patients of different genders, ages, pathological types and tumor diameters (
p > .05) (see
Tables 10-
14).
3.4 The value of ALP, N-MID and other markers in diagnosing bone metastasis
Pathological examination serves as the gold standard for diagnosing bone metastasis. The areas under the ROC curves for ALP, N-MID and TPINP in diagnosing bone metastasis were 0.695, 0.734 and 0.837, respectively, with
p < .05. The area under the curve (95% CI) for lumbar spine BMD was 0.587 (0.470–0.704),
p = .139, indicating no statistically significant diagnostic value for bone metastasis. Specific parameters are shown in
Table 15.
4. Discussion
Patients with bone metastasis frequently suffer from bone pain and skeletal-related events (SREs), including pathological fractures and spinal cord compression. The optimal treatment aims to delay the progression of bone metastasis, alleviate pain, prevent SREs and improve quality of life. It is difficult to assess the objective response of metastatic bone lesions to systemic therapies such as endocrine and cytotoxic treatments.
[7] X-ray examination is the most convenient and economical routine method for bone assessment. However, it is not sensitive to small bone metastasis measuring less than 1 cm. While osteolytic or mixed osteolytic-osteoblastic bone metastasis can be measured and quantified via CT and MRI, osteoblastic metastasis cannot be detected by these imaging modalities.
[8] Bone scans are a representative imaging modality for diagnosing and evaluating bone abnormalities, including bone metastasis, and assessing treatment response. However, the diagnosis of bone metastasis is primarily based on the macroscopic assessment, which can only identify the location, size, shape, and number on imaging studies, and relies heavily on the physician’s experience.
[9] Although this is a highly useful method, the diagnostic capability of whole-body imaging is generally considered inferior to SPECT. SPECT can reveal dense phenomena in bone trauma, inflammation, degeneration, and other lesions, which may be misdiagnosed as cancerous bone metastasis, leading to false positive results.
[10] The initial stage of bone metastasis exhibits only limited skeletal anatomical changes, which can be detected using SPECT/CT. SPECT/CT has been demonstrated to enhance the specificity and positive predictive value of bone scans, offering diagnostic value beyond conventional bone imaging.
[11] This study found that lumbar spine BMD was significantly lower in patients with bone metastasis in comparison to those without bone metastasis (
p < .05), while no significant differences were observed in femoral neck BMD or whole-body BMD. Evidence indicates that bone metastasis is associated with significant bone resorption and bone loss, with the lumbar spine potentially being more susceptible to bone metastasis. This may be related to certain osteolytic substances produced by tumor cells, such as prostaglandins, which can activate osteoclasts and increase bone resorption. Because the lumbar spine is located along the longitudinal axis of human body and plays a role in significant daily activities, it has a relatively rich blood supply, increasing the likelihood of bone metastasis.
SUV is a viable semi-quantitative parameter representing the tracer concentration corrected for body weight and injection activity. It is commonly used to assess the uptake of radionuclide tracers, reflecting the proliferation rate and metabolic activity of tumor tissue. It greatly aids in disease diagnosis, treatment efficacy evaluation and prognosis determination.
[8, 12] Our study found that adenocarcinoma patients exhibited significantly lower SUVmax values in comparison to patients with squamous cell carcinoma and other types (
p < .05); tumor diameter and TNM staging were independent factors influencing SUVmax. Patients with tumors > 5 cm in diameter and TNM stage III-IV demonstrated significantly higher SUVmax values in comparison to those with tumors ≤ 5 cm in diameter and TNM stage I-II (
p < .05). Patients with tumors that are larger and at later stages may be more prone to bone metastasis. The higher SUVmax values observed in squamous cell carcinoma in comparison to adenocarcinoma may be attributed to the overexpression of glucose transporter-1 (GT-1) in squamous cell carcinoma cells, which results in a shorter doubling time and faster proliferation rate. Patients with tumors that are larger and at later stages exhibit relatively faster proliferation rates and higher metabolic activity, resulting in relatively higher SUVmax values.
Among various bone turnover markers, ALP is the most widely used marker of bone remodeling. Its advantage is that it is easier and less expensive to measure than other bone turnover markers. ALP is located in the osteoblast membrane and represents osteoblast activity.
[13] Osteocalcin is a specific non-collagenous protein secreted by osteoblasts, with approximately one-third hydrolyzed into N-MID in peripheral blood. N-MID serves as a specific marker reflecting osteoblast activity, bone formation, and bone remodeling. TPINP is a specific type I collagen deposition marker that serves as an indicator of bone formation, with its levels significantly elevated during the occurrence of bone metabolic diseases. Our study found that ALP, N-MID and TPINP levels were significantly higher in patients with TNM stage III-IV in comparison to those with TNM stage I-II (
p < .05). The areas under the ROC curves for ALP, N-MID and TPINP in diagnosing bone metastasis were all greater than 0.05, with TPINP (0.837) showing the highest value (
p < .05). It indicates that patients in advanced stages are more prone to bone metastasis. ALP, N-MID and TPINP may serve as important biomarkers for distinguishing tumor staging and diagnosing bone metastasis, with TPINP demonstrating higher diagnostic value for bone metastasis. In advanced patients, tumor proliferation is rapid, making bone metastasis more likely to occur. Due to tumor invasion, osteoblast activity and metabolism become abnormal, leading to the elevated levels of ALP, N-MID and TPINP.
5. Conclusions
Serum levels of ALP, N-MID and TPINP are significantly elevated in patients with lung cancer bone metastasis in comparison to those without bone metastasis, while SUVmax shows no significant difference. SUVmax, ALP, N-MID and TPINP are associated with certain clinical and pathological characteristics in lung cancer patients. Among these, ALP, N-MID and TPINP demonstrate potential diagnostic value for lung cancer bone metastasis.
Authors contributions
Hong Gu contributed to the study design and argumentation, literature search, data acquisition and organization, manuscript drafting; Guowei Tan and Qinghe Yu contributed to the data measurement on the subjects, data statistics and summary.
Funding
The study was funded by the Health and Hygiene Research Project of the Metallurgical Safety and Health Branch of the China Metallurgical Society (No. jkws202368).
Conflicts of Interest Disclosure
The authors declare no conflicts of interest.
Informed consent
Obtained.
Ethics approval
The journal’s policies adhere to the Core Practices established by the Committee on Publication Ethics (COPE).
Provenance and peer review
Not commissioned; externally double-blind peer reviewed.
Data availability statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
Data sharing statement
No additional data are available.
Open access
This is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).
Copyrights
Copyright for this article is retained by the author(s), with first publication rights granted to the journal.
PDF
(1001KB)
