Procollagen type III aminoterminal peptide in serum in idiopathic myelofibrosis and allied conditions: relation to disease activity and effect of chemotherapy

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

Bone marrow fibrosis: pathophysiology and clinical significance of increased bone marrow stromal fibres

In bone marrow biopsies, stromal structural fibres are detected by reticulin and trichrome stains, routine stains performed on bone marrow biopsy specimens in diagnostic laboratories. Increased reticulin staining (reticulin fibrosis) is associated with many benign and malignant conditions while increased trichrome staining (collagen fibrosis) is particularly prominent in late stages of severe myeloproliferative diseases or following tumour metastasis to the bone marrow. Recent evidence has shown that the amount of bone marrow reticulin staining often exhibits no correlation to disease severity, while the presence of type 1 collagen, as detected by trichrome staining, is often associated with more severe disease and a poorer prognosis. It was originally thought that increases in bone marrow stromal fibres themselves contributed to the haematopoietic abnormalities seen in certain diseases, but recent studies suggest that these increases are a result of underlying cellular abnormalities rather than a cause. A growing body of evidence suggests that increased deposition of bone marrow stromal fibres is mediated by transforming growth factor-beta and other factors elaborated by megakaryocytes, but it is likely that other cells, cytokines and growth factors are also involved. This suggests new avenues for investigation into the pathogenesis of various disorders associated with increased bone marrow stromal fibres.

Elevated plasma levels of TIMP-1 correlate with plasma suPAR/uPA in patients with chronic myeloproliferative disorders

Chronic myeloproliferative disorders (MPD) are characterized by progressive remodelling of bone marrow stroma as evidenced by increased deposition of extracellular matrix proteins, neoangiogenesis and displacement of normal haematopoietic cells by fibrotic tissue. The family of metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) serve to facilitate and inhibit matrix degradation processes, respectively. In an attempt to investigate potential markers for bone marrow remodelling processes, we investigated plasma levels of total-, free- and complexed TIMP-1, TIMP-2, MMP-2 and MMP-9 in a patient cohort comprising 17 with myelofibrosis (MF), 17 with polycythaemia vera (PV), 15 with essential thrombocythaemia (ET), 1 with a transitional MPD and 30 controls. Compared with controls, total- (P < 0.0001) (median: 132.6 microg/L vs. 80.8 microg/L), free- (P < 0.0001) (median: 126.4 microg/L vs. 65.8 microg/L) and complexed TIMP-1 (P = 0.0009) (median: 17.7 microg/L vs. 10.7 microg/L) concentration was significantly higher in the patients. TIMP-1 was significantly correlated with plasma soluble urokinase plasminogen activator receptor (P = 0.003) and urokinase plasminogen activator (P < 0.0001), respectively, suggesting a common cellular origin. No statistical significant difference between TIMP-2 and MMP-2 levels was observed between patients and controls. Furthermore, a significant correlation between free TIMP-1 and TIMP-2 levels was detected (r = 0.56; P < 0.0001). Median MMP-9 concentration was significantly higher among PV patients compared with controls (P = 0.0015), and 41% of patients with PV (7/17) had MMP-9 values that were above the mean + 2SD of plasma MMP-9 levels found in controls. The ratio of total TIMP-1/MMP-9 was significantly higher in patients with MF compared with controls (P = 0.0004). These findings suggest that a disturbed TIMP-1/MMP ratio may reflect an imbalance of the extracellular homeostasis towards an increased matrix deposition promoting fibrosis.

Collagen metabolism and enzymes of the urokinase plasminogen activator system in chronic myeloproliferative disorders: correlation between plasma-soluble urokinase plasminogen activator receptor and serum markers for collagen metabolism

Extracellular proteolytic enzymes of the urokinase-type plasminogen activator (uPA) system and the family of metalloproteinases (MMPs) catalyse the matrix degradation and remodelling processes characteristic of invasive malignant disorders. In a cohort of 50 patients with chronic myeloproliferative disorders (MPD) serum markers for collagen metabolism were compared to plasma levels of enzymes of the uPA and MMP system. Serum aminoterminal propeptide of type III procollagen (S-PIIINP) (P < 0.0001) concentration was significantly higher in the patients (median 3.7 micro g/L vs. 2.5 micro g/L) compared with controls. In a subgroup analysis comprising patients with myelofibrosis (MF), polycythaemia vera (PV) and essential thrombocythaemia (ET), respectively, S-PIIINP levels differed significantly with the highest values found in patients with MF (MF vs. PV vs. ET; P = 0.0027). Serum concentration of carboxyterminal telopeptide of type I collagen (S-ICTP) (P = 0.0006), reflecting type I collagen degradation, was significantly higher in patients compared with controls (median 4.0 micro g/L vs. 2.7 micro g/L). When comparing S-ICTP measurements between patient subgroups and controls there were only significantly higher values among MF and PV patients (MF vs. controls; P < 0.0001, PV vs. controls; P = 0.0016). A significant correlation between the marker for collagen synthesis (S-PIIINP) and degradation (S-ICTP) (r = 0.59; P < 0.0001) was demonstrated. A correlation analysis between serum markers for bone marrow remodelling processes (S-PIIINP, S-ICTP and S-hyaluronan) and plasma-soluble urokinase plasminogen receptor (suPAR) disclosed a significant relationship between suPAR and S-PIIINP (r = 0.48; P = 0.0009), S-hyaluronan (r = 0.56; P < 0.0001) and S-ICTP (r = 0.47; P = 0.0013), respectively. Plasma levels of MMP-2 and -9 were not correlated to serum markers for collagen metabolism. These findings suggest that enzymes of the uPA system might participate in the bone marrow remodelling processes characteristic of MPD.

Interferon-alpha treatment decreases serum cross-linked C-terminal telopeptide of type I collagen in haematological diseases

Interferon-alpha (IFN-alpha) is used in the treatment of many haematological diseases and it is known that IFN-alpha may affect bone turnover. The effect of IFN-alpha on bone metabolism was studied in 10 haematological patients. The mean duration of the treatment was 4 (range: 2.8-7.2) months. Besides the usual markers of bone metabolism, levels of the cross-linked C-terminal telopeptide of type I collagen (ICTP), the N-terminal propeptide of type I procollagen (PINP) and the bone-specific alkaline phosphatase were measured. The bone mineral density was measured by computed tomography. During IFN-alpha treatment, serum ICTP decreased from a mean of 5.4 (range: 1.8-12.4) to 3.6 (range: 1.4-8.8) microg/l (P = 0.017). All other variables reflecting bone metabolism remained unaltered during IFN-alpha treatment. The bone mineral density remained unchanged. It was concluded that the observed decrease in ICTP may be an indicator of a beneficial therapeutic effect of IFN-alpha on bone turnover, resulting in decreased bone resorption. However, it is possible that elevated pretreatment ICTP values reflected disease of the bone marrow.

Abnormal bone turnover in monoclonal gammopathy of undetermined significance: analyses of type I collagen telopeptide, osteocalcin, bone-specific alkaline phosphatase and propeptides of type I and type III procollagens

The main difference between monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) is the presence of lytic bone destructions in the latter. About 20% of MGUS patients develop MM, and histomorphometric studies have shown disturbed bone turnover rates in some of these patients. This study was performed in order to evaluate whether serum analyses of the C-terminal telopeptide of type I collagen (ICTP), as a reflector of bone degradation, and of osteocalcin, bone-specific alkaline phosphatase (bAP) and the C-terminal propeptide of type I procollagen (PICP), as markers of bone formation, might give information on disturbances of bone metabolism in MGUS. Furthermore, serum N-terminal propeptide of procollagen III (PIIINP) might give information on disturbances in collagen III metabolism in the bone marrow. In the 35 patients examined, serum ICTP was elevated in 12 patients (34%), serum PIIINP elevated in 6 patients (17%), serum osteocalcin elevated in 11 patients (31%), serum bAP elevated in 6 patients (17%), and serum PICP elevated in 4 patients (11%). Serum ICTP correlated significantly with PIIINP (r = 0.72, p < 0.001), and with serum osteocalcin (r = 0.57, p < 0.001) and serum bAP (r = 0.51, p = 0.002). These findings indicate disturbances of bone turnover and affected collagen metabolism in some MGUS patients. Follow-up observation may reveal any prognostic value of these findings.

Markers of type I collagen degradation and synthesis in the monitoring of treatment response in bone metastases from breast carcinoma

Thirty-six patients with bone metastases included in a trial of supportive calcitonin on the treatment response to systemic therapy were monitored by conventional radiography, conventional indicators of bone metabolism [alkaline phosphatase (AP), osteocalcin (gla), urinary hydroxyproline excretion (OHP), urinary calcium (uCa), serum calcium (sCa)] and collagen metabolites (ICTP, the pyridinoline cross-linked carboxy-terminal telopeptide of type I collagen; PICP, the carboxy-terminal propeptide of type I procollagen; and PIIINP the amino-terminal propeptide of type III procollagen). All patients had been on the same systemic treatment for at least 3 months at the start of the trial. There was a positive correlation between the concentrations of ICTP and PICP at baseline (Spearman's rank-order correlation coefficient rs = 0.62). Both ICTP and PICP showed statistically significant correlations to the other markers of bone metabolism (except sCa and uCa) as well as to the number of bone metastases on bone scans. Reduction in ICTP correlated significantly with the treatment response at three months (rs = - 0.57). while PICP showed a borderline negative correlation to therapy response (rs = - 0.37). Of all the biochemical parameters studied the changes in ICTP showed the best correlation with the treatment response. PICP and ICTP changes in patients with progressive disease differed significantly from those in patients with responding and stable metastases, whereas no difference was found between responders and stable patients.

Evans' syndrome, myelofibrosis and systemic lupus erythematosus: role of procollagens in myelofibrosis

We describe an 18 yr old female with systemic lupus erythematosus presenting with Evans' syndrome (autoimmune hemolytic anemia and immune thrombocytopenia) and dense myelofibrosis. Her clinical course and response to treatment were monitored with regular blood counts, serial measurements of serum procollagen I and III and periodic bone marrow examinations. This report brings to 9 the number of well-documented cases of systemic lupus erythematosis and myelofibrosis in the literature; we discuss the pathogenesis and management of patients with this apparently rare disorder, with particular reference to the role of serum procollagen measurements as markers of myelofibrosis.

Bone marrow and serum connective tissue polypeptides in idiopathic myelofibrosis

The distribution of collagen type VI and tenascin has been determined in both normal and myelofibrotic bone marrow by immunohistological techniques. In normal sections positivity was demonstrated in the periosteum (collagen type VI and tenascin) and in the walls of small blood vessels (tenascin). In contrast, myelofibrotic bone marrow showed an increased deposition of both proteins, especially collagen type VI, although this increase was restricted to the later fibrotic stages of the disease. Serum concentrations of collagen type I (PICP), collagen type III (PIIIP) and laminin (laminin P1) related polypeptides were determined in a further 26 patients. PIIIP levels were significantly raised, in contrast to PICP and laminin P1 concentrations. All three markers, however, were significantly elevated in patients with active/transforming disease. Laminin P1 and PICP levels showed a strong correlation, indicating a relationship between basement membrane and interstitial collagen metabolism, although they do not appear to offer any advantage over PIIIP for the monitoring of disease activity.

CYP3A4 and CYP2A6 activities marked by the metabolism of lignocaine and coumarin in patients with liver and kidney diseases and epileptic patients

1. The in vitro hepatic metabolism of lignocaine to monoethylglycinexylide (MEGX) is mediated by CYP3A4 and that of coumarin to 7-hydroxycoumarin (7OHC) by CYP2A6. We investigated the usefulness of monitoring serum MEGX concentrations (after 1 mg kg-1 lignocaine i.v.) and urinary 7OHC excretion (after 5 mg coumarin p.o.) to reflect liver function in patients with liver (n = 36), kidney (n = 12) and epileptic (n = 12) disease and in control subjects (n = 20). The extent of liver disease was assessed using measurements of serum aminoterminal propeptide (PIIINP) and Child-Pugh grades. 2. Serum concentrations of MEGX were decreased in severe (4.6 +/- 3.0 s.d. ng ml-1), moderate (19.1 +/- 11.6 s.d. ng ml-1) and mild (32.8 +/- 14.2 s.d ng ml-1) liver disease as compared with controls (53.4 +/- 15.8 s.d ng ml-1). The excretion of 7OHC over 2 h was decreased in severe (18.0 +/- 10.3 s.d % of dose) and moderate (34.2 +/- 15.6 s.d %), but not in mild (49.7 +/- 19.0 s.d %) liver disease as compared with that in controls (56.2 +/- 11.6%). 3. In epileptic patients the urinary recovery of 7OHC was increased (2 h value 69.5 +/- 13.2 s.d %) suggesting enzyme induction. In contrast, serum MEGX concentration were low (40.0 +/- 14.1 s.d ng ml-1), possibly due to competition for CYP3A4 between lignocaine and antiepileptic drugs. 4. In patients with kidney disease serum MEGX concentration (56.5 +/- 26.1 s.d ng ml-1) was similar to that in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-alpha 2a increases serum concentration of hyaluronic acid and type III procollagen aminoterminal propeptide in patients with chronic hepatitis B virus infection

Interferon-alpha (IFN-alpha) has become an important drug for the treatment of chronic viral liver diseases. However, the action of IFN-alpha remains unclear. We investigated whether human recombinant IFN-alpha modulates serum concentrations of hyaluronic acid (HA) and type III procollagen aminoterminal propeptide (P-III-NP) in 56 patients with chronic hepatitis-B under IFN-alpha therapy. IFN-alpha increased the HA serum level in 44 of 46 patients and, after cessation of treatment, HA serum levels returned to the pretherapy levels. The increase of HA serum level was higher in patients with active cirrhosis (aC) than in patients with chronic persistent hepatitis (CPH) and in patients with severe inflammation compared to those with moderate inflammation. Interestingly, HA serum concentration was unrelated to IFN dose and was of no predictive value for therapy response. In contrast, IFN-alpha increased significantly the P-III-NP serum level in patients with aC only. During follow-up, P-III-NP serum level decreased late in responders in parallel to the decrease of serum level of liver enzymes, in non-responders it was without significant change. The first dose of IFN induced a significant increase in HA serum level in each of 10 patients but in none of four healthy volunteers. In contrast, P-III-NP serum concentrations were not influenced by the first IFN-alpha dose. We conclude that: (1) immunstimulation with IFN-alpha induces a rapid increase of HA serum level in patients with chronic hepatitis B but not in normal persons; (2) IFN-alpha increases P-III-NP serum level only in patients with active liver cirrhosis; (3) measurement of HA and P-III-NP serum levels does not help predict response to IFN-alpha, and (4) HA serum level may be used as a compliance indicator.

Serum laminin P1 in idiopathic myelofibrosis and related diseases

The serum concentration of laminin P1 antigen was determined in 32 patients with various myeloproliferative disorders, including 19 patients with idiopathic myelofibrosis. The serum concentration of the aminoterminal propeptide of type III procollagen (PIIINP) was measured concomitantly in 27 patients. Serial laminin measurements were carried out in 25 patients. The median serum laminin concentration in patients with acute disease, i.e. acute myelofibrosis and patients in a transforming disease phase was significantly higher (1.58 U/ml; range 1.15-2.07) as compared with patients with chronic disease (1.02 U/ml; range 0.75-1.76; p = 0.012) and healthy control subjects (1.13 U/ml; range 0.75-1.67; p = 0.00015). In individual patients serum laminin covariated closely with serum PIIINP, the leucocyte count and LDH. The median serum laminin concentration in patients with a huge spleen was significantly lower than in the patient group with a normal spleen size/previous splenectomy. Pronounced splenomegaly was particularly prevalent in patients with chronic disease implicating splenic enlargement as a significant extrahepatic site of laminin uptake/degradation in myeloproliferative disorders.

Connective tissue components in serum in multiple myeloma: analyses of propeptides of type I and type III procollagens, type I collagen telopeptide, and hyaluronan

The present study was performed to evaluate whether information concerning synthesis and degradation of type I collagen in multiple myeloma (MM) as obtained by serum analyses of C-terminal propeptide of type I procollagen (PICP) and the C-terminal telopeptide of type I collagen (ICTP) may be useful in evaluating the development of osteolytic bone destruction. Serum N-terminal propeptide of type III procollagen (PIIINP) may give information about marrow fibrosis in MM. No data are available about MM and serum hyaluronan, another important component of bone marrow stroma. We examined 15 consecutive patients before treatment and 15 sex- and age-matched controls. We found highly significant elevations in serum ICTP (median 6.2 vs. 2.4 micrograms/L; P < 0.01), PIIINP (median 5.2 vs. 2.9 micrograms/L; P < 0.01) and hyaluronan (median 122 vs. 45 micrograms/L; P < 0.01). ICTP in serum correlated closely to bone morbidity (r = 0.69; P < 0.01). Furthermore, serum ICTP correlated highly significantly to serum PIIINP (P < 0.01) and serum beta 2-microglobulin (P < 0.01), whereas there was no correlation between hyaluronan and any of the collagen-derived peptides or beta 2-microglobulin. The MM group was followed for 9-25 months and analysis of survival data suggested that serum ICTP may be of predictive value (P < 0.05). We conclude that important changes in connective tissue metabolism occur in MM. ICTP in serum seems to be a noninvasive marker of bone morbidity and may be of prognostic value. Furthermore, elevation of hyaluronan in serum is common in MM, the significance of which is unknown.

Antibodies against terminal galactosyl alpha(1-3) galactose epitopes in patients with idiopathic myelofibrosis

Sera from patients with myelofibrosis were analysed for circulating antibodies against an antigenic determinant characterized by two molecules of galactose in alpha 1-3 linkage (anti-Gal antibodies). 50% of patients were found to have values above the 90th percentile of the values of control sera chosen as a cut-off. The median level of the antibodies was significantly higher than the value detected in normal controls, but no difference could be found between patients with idiopathic myelofibrosis and those with myelofibrosis associated to a chronic myeloproliferative disorder. Anti-Gal antibodies were found to correlate with disease activity and with platelet count whereas no correlation was detected with other haematological parameters. Furthermore, for evaluation of disease activity, determination of serum anti-Gal antibodies was a sensitive and specific parameter. We conclude that humoral immunity against Gal alpha 1-3Gal may provide a sensitive tool to detect disease activity in patients with idiopathic myelofibrosis and may be important for understanding its pathogenesis.

Characterization of an acute micromegakaryocytic leukaemia: evidence for the pathogenesis of myelofibrosis

The current hypothesis for the pathogenesis of myelofibrosis involves the intramedullary release of growth factors from defective or abnormal megakaryocytes. We describe a case of an acute micromegakaryocytic leukaemia, in a patient with chronic myelofibrosis, that provides additional evidence for this concept. The micromegakaryocytes, which reached 223 x 10(9)/l, were characterized morphologically by both light and electron microscopy, immunocytochemically and by platelet peroxidase activity. The cells were shown to have a mature cytoplasm, containing alpha granules and the associated proteins; vWF:Ag, fibrinogen, fibronectin and protein S. DNA analysis, by both a Seescan Solitaire Plus image analysis system and flow cytometry, revealed nuclear immaturity, with 92% of cells being diploid. Serum markers of connective tissue synthesis, namely carboxy terminal peptide of procollagen I (PICP), procollagen terminal peptide III (PIIIP) and laminin all increased significantly following transformation and were associated with an increase in platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta). These observations support the current hypothesis for bone marrow fibrosis formation and provide, for the first time, a link between in vivo growth factor release, bone marrow stromal turnover and megakaryocyte mass. In addition, the release of biologically active TGF-beta may explain both the increased fibronectin and angiogenesis characteristic of myelofibrotic bone marrow.

Monitoring of multiple myeloma and bone marrow fibrosis with aminoterminal propeptide of type III collagen (PIIINP)

Bone marrow fibrosis is known in myelomatosis and depends on the extent of plasma cell infiltration. The serum concentration of the aminoterminal propeptide of type III procollagen (PIIINP) has previously been reported to reflect fibrogenesis in the marrow in myelofibrosis. Here we followed 15 consecutive patients with newly diagnosed multiple myeloma with repeated PIIINP measurements during treatment with intermittent courses of melphalan and prednisolone. PIIINP was found to change with clinical behaviour of the disease, nonresponders and patients with recurrent disease having elevated values and the values in responders decreasing to the normal level or remaining there. Collagen fibres in plasma cell infiltrates of biopsies from bone marrow or skeletal tumours of these patients stained heavily with antibodies against PIIINP. Our results suggest that PIIINP works as a noninvasive indicator of bone marrow fibrogenesis. In multiple myeloma PIIINP is a sensitive, but not specific marker of disease course.

Hypercalcemia in idiopathic myelofibrosis: modulation of calcium and collagen homeostasis by 1,25-dihydroxyvitamin D3

A case of idiopathic myelofibrosis (IMF) presenting with hypercalcemia and hypercalcitriolemia is reported. It is proposed that ectopic production of the active vitamin D metabolite related to ongoing clonal expansion in the bone marrow accounts for the hypercalcemic state. Consistently low levels of circulating type I procollagen propeptide (PICP) and lack of progression of the bone marrow fibrosis during almost 6 months of follow-up point to an in vivo inhibition of type I collagen synthesis by 1,25-dihydroxyvitamin D3.

A sequential histological study of bone marrow fibrosis in idiopathic myelofibrosis

A sequential histological study of bone marrow biopsies from 36 patients with idiopathic myelofibrosis was performed to investigate the accumulation of connective tissue in the bone marrow during the course of the disease and the influence of therapy on this process. The degree of bone marrow fibrosis was graded semiquantitatively from 0 (normal) to +5 (extensive collagen fibrosis and ostemyelosclerosis). The median interval between the first and final biopsy was 25 months (range 3 to 103) in patients with chronic idiopathic myelofibrosis and 2 months (range 1 to 14) in patients with a syndrome of acute myelofibrosis. In most patients with chronic IMF the bone marrow fibrosis remained unchanged. Regression of bone marrow fibrosis in 9 patients with chronic IMF was associated with immunosuppressive/-cytotoxic treatment or splenectomy. Severe bone marrow fibrosis completely resolved during intensive chemotherapy of a patient with acute myelofibrosis. No relationship existed between spleen size and the degree of bone marrow fibrosis.

Bone marrow stroma in idiopathic myelofibrosis and other haematological diseases. An immunohistochemical study

Bone marrow stroma was investigated immunohistochemically in 31 patients with haematological diseases, mainly idiopathic myelofibrosis (n = 8) and related chronic myeloproliferative disorders (n = 14). The bone marrow from patients with idiopathic myelofibrosis and some CML patients showed marked staining reactions with antibodies against type III procollagen (pN collagen), type IV collagen, fragment P1 of laminin and factor VIII. Patients with osteomyelosclerosis had particularly increased collagen content, including both newly deposited type III collagen (pN collagen) and mature collagen fibres. As in normal bone marrow, argyrophilic fibres and type III collagen displayed a close co-distribution, which was also demonstrated for type IV collagen and laminin. While normal bone marrow sinusoids had discontinuous basement membranes, fibrosing bone marrow was characterized by endothelial cell proliferation and capillarization, with the development of continuous sheets of basement membrane material beneath endothelial cells.

Circulating hyaluronan in the myelofibrosis/osteomyelosclerosis syndrome and other myeloproliferative disorders

The serum concentration of hyaluronan (HYA) was determined in 59 patients with various myeloproliferative disorders, including 33 patients with idiopathic myelofibrosis. In 18 patients the serum concentration of the aminoterminal propeptide of type III procollagen (PIIINP) was measured concomitantly. Raised serum HYA levels were seen in patients with active disease compared with age-matched healthy subjects, whereas no significant difference in serum HYA was seen between patients with stable disease and age-matched controls. Serum HYA concentrations correlated significantly with the leukocyte count (rho = 0.38; P less than 0.02) and with the serum concentration of PIIINP (rho = 0.50; P less than 0.001). During cytotoxic treatment, the serum HYA and PIIINP concentrations decreased in concert with declining leukocyte counts. These findings suggest that clonal expansion is accompanied by a bone marrow stromal reaction similar to the repair processes following injury to soft connective tissues. The relatively modest changes in serum HYA with frequent overlaps between patient categories and healthy subjects imply that the clinical utility of single determinations of serum HYA in the present disease groups is restrained. On the other hand, sequential measurements of HYA may provide a reflection of the myeloproliferative process in individual patients.