Classification of pleomorphic sarcomas: where are we now?

Malignant fibrous histiocytoma of the head and neck region

BACKGROUND

Malignant fibrous histiocytoma (MFH) is 1 of the most common soft tissue sarcomas in the head and neck.

METHODS

We conducted a retrospective review of patients with MFH of the head and neck region at a large multidisciplinary cancer center between 1973 and 2005.

RESULTS

Ninety-five patients were included in the study. The median age at diagnosis was 53 years (range, 3-90 years); 69% of the patients were men. The parotid or neck was the most common subsite (35%), and 23% of the cases were associated with prior radiation exposure. Although there were no significant differences in the distribution of age, sex, year of presentation, tumor location, size, local extension, or treatment between patients with and without prior radiation exposure, those with radiation-associated tumors were more likely to have positive or unclear surgical margins (p = .037). With a median follow-up of 34 months, 32 (39%) of the 83 patients treated at M. D. Anderson Cancer Center with curative intent had a recurrence (isolated local recurrence in 18, isolated distant recurrence in 8, both local and distant recurrence in 5, and regional recurrence in 1). For patients treated at our institution with curative intent, 5-year overall, disease-free, and disease-specific survival rates were 55%, 44%, and 69%, respectively. Prior radiation exposure and positive margins were associated with worse survival.

CONCLUSION

MFH of the head and neck region is often aggressive and characterized by local and/or distant recurrence and poor survival. Radiation-associated tumors seem to have an especially poor prognosis. Based on a significant body of literature, multidisciplinary evaluation and treatment of such high-grade sarcomas is encouraged.

Transformation potential of bone marrow stromal cells into undifferentiated high-grade pleomorphic sarcoma

PURPOSE

Bone marrow adherent cells contain conventional bone marrow stromal cells and mesenchymal stem cells and these cells constitute the hematopoietic microenvironment. Mesenchymal stem cells have the capacity to give rise to multiple mesenchymal lineage cells and even ectodermal lineage cells. In the present study, we investigated what types of tumor cells are inducible from BM adherent cells by chemical carcinogens.

METHODS

Bone marrow cells from neonatal C3H/HeN mice were collected within 24 h after birth and then cultured. Four days later, bone marrow adherent cells were obtained and the cells were treated with 3-methylcholanthrene.

RESULTS

By this treatment, some transformed clones consisting of large spindle cells were obtained. The transformed cells were highly positive for CD44 and were positive for Sca-1, CD49d and CD106, whereas the cells were negative for hematolymphoid markers. The cell clones had the ability to support hematopoiesis in vitro. These results indicate that the transformed cell lines have the characteristics of BM stromal cells/mesenchymal stem cells. Moreover, during culture of the transformed cells, spontaneous bone nodule formation was observed. When the transformed cells were inoculated into immunodeficient mice subcutaneously, the neoplasms grew in the subcutaneous tissue of the mice. Microscopically and ultrastructurally, the neoplasms showed the typical morphology of undifferentiated high-grade pleomorphic sarcoma (UHGPS). Bone-related genes have been found to be expressed in both transformed cells and UHGPSs.

CONCLUSION

The present study suggests that UHGPSs are derived from BM stromal cells, probably mesenchymal stem cells.

Malignant fibrous histiocytoma complicating nephrogenic systemic fibrosis post liver transplantation

A 46-year-old man with cirrhosis secondary to hepatitis C virus infection and alcohol underwent orthotopic liver transplantation, which required urgent re-grafting because of biliary sepsis from necrosis of the left liver lobe. Recovery was complicated by renal failure and nephrogenic systemic fibrosis (probably related to intravenous gadolinium exposure). He subsequently developed a malignant fibrous histiocytoma. We present this case highlighting the occurrence of two rare conditions in the same patient following liver transplantation. We believe this is the first case of its kind to be reported.

Soft tissue sarcomas with complex genomic profiles

Soft tissue sarcomas (STS) with complex genomic profiles (50% of all STS) are predominantly composed of spindle cell/pleomorphic sarcomas, including leiomyosarcoma, myxofibrosarcoma, pleomorphic liposarcoma, pleomorphic rhabdomyosarcoma, malignant peripheral nerve sheath tumor, angiosarcoma, extraskeletal osteosarcoma, and spindle cell/pleomorphic unclassified sarcoma (previously called spindle cell/pleomorphic malignant fibrous histiocytoma). These neoplasms show, characteristically, gains and losses of numerous chromosomes or chromosome regions, as well as amplifications. Many of them share recurrent aberrations (e.g., gain of 5p13-p15) that seem to play a significant role in tumor progression and/or metastatic dissemination. In this paper, we review the cytogenetic, molecular genetic, and clinicopathologic characteristics of the most common STS displaying complex genomic profiles. Features of diagnostic or prognostic relevance will be discussed when needed.

MFH classification: differentiating undifferentiated pleomorphic sarcoma in the 21st Century

The essence and origin of malignant fibrous histiocytoma (MFH) have been debated for now close to five decades. Originally characterized as a morphologically unique soft-tissue sarcoma subtype of unclear etiology in 1963, with a following 15 years of research only to conclude that "the issue of histogenesis [of MFH] is largely unresolvable"; it is "now regarded as synonymous with [high grade] undifferentiated pleomorphic sarcoma and essentially represents a diagnosis of exclusion". Yet despite this apparent lack of progress, the first decade of the 21st century has seen some significant progress in terms of defining the origins of MFH. Perhaps more importantly these origins might also pave the way for novel therapies. This manuscript will highlight MFH's troubled history, discuss recent advances, and comment as to what the coming years may promise and what further needs to be done to make sure that progress continues.

Secondary malignant fibrous histiocytoma following refractory langerhans cell histiocytosis

We describe a rare case of secondary malignant fibrous histiocytoma (MFH) following Langerhans cell histiocytosis (LCH). A 23-year-old Japanese male exhibited systemic lymphadenopathy, multiple lung tumors, and osteolytic changes in bilateral iliac bones in 1989. A biopsy specimen from the left iliac bone revealed an infiltration of S-100 protein-positive histiocyte-like cells intermingled with eosinophils, which confirmed the diagnosis of eosinophilic granuloma, a type of LCH. Although the patient was treated with prednisolone initially, the disease did not respond well and progressed gradually over time. The patient subsequently received multiple courses of chemotherapy and immunosuppressive therapy with many kinds of anticancer agents for 6 years. He also received radiotherapy totaling 136.8 Gy for lung tumors and osteolytic lesions of the pelvis. In 1997, because of the LCH refractoriness, biopsy was performed again from the right inguinal lymph node. Microscopic examinations demonstrated a mixture of spindle-shaped cells and histiocyte-like cells, which appeared to be in a storiform pattern. The tumor cells were immunohistologically positive for CD68 and vimentin, but negative for CD1a and S-100 protein. Therefore, the patient was diagnosed with MFH. Although chemotherapy was continued, the patient died of pneumonia during the neutropenic period following chemotherapy. Autopsy revealed systemic invasion of MFH and dissemination of mucormycosis. LCH was not detected histologically in any tissues.

Gene expression profiling for the investigation of soft tissue sarcoma pathogenesis and the identification of diagnostic, prognostic, and predictive biomarkers

Soft tissue sarcomas are malignant neoplasms derived from mesenchymal tissues. Their pathogenesis is poorly understood and there are few effective treatment options for advanced disease. In the past decade, gene expression profiling has been applied to sarcomas to facilitate understanding of sarcoma pathogenesis and to identify diagnostic, prognostic, and predictive markers. In this paper, we review this body of work and discuss how gene expression profiling has led to advancements in the understanding of sarcoma pathobiology, the identification of clinically useful biomarkers, and the refinement of sarcoma classification schemes. Lastly, we conclude with a discussion of strategies to further optimize the translation of gene expression data into a greater understanding of sarcoma pathogenesis and improved clinical outcomes for sarcoma patients.

NF1 diagnosis criteria and associated sarcomatous tumor review of the literature and case report

AIM

This paper reports the case of a sarcomatous tumor (probably a pleomorphic sarcoma) in a patient with Neurofibromatosis type 1 (NF1) and discusses the association between these two diseases.

BACKGROUND

NF1 is an autosomal dominant tumor predisposition syndrome. Malignant transformation is observed in patients with this disease, usually in the form of malignant peripheral nerve sheath tumors (MPNSTs).

REPORT

A 72-year-old female patient with diagnosis of NF1 presented with left mandibular region enlarged for about 6 months, intra-oral examination revealed a mass growth on the floor of the lower left posterior area of the oral cavity measuring 5 cm in its greatest diameter and covered by ulcerated mucosa.

SUMMARY

Few cases of association of neurofibromatosis with other types of soft tissue sarcomas have been reported. Undifferentiated pleomorphic sarcomas are the most common of these tumors. We intend to call attention to the importance of patient follow-up and counseling.

Malignant fibrous histiocytoma--pleomorphic sarcoma, NOS gene expression, histology, and clinical course. A pilot study

PURPOSE

The new classification of malignant fibrous histiocytoma leaves only a small group of tumors without further line of differentiation, so-called pleomorphic sarcomas, not otherwise specified (NOS) as a pseudo-entity. This study focused on these tumors and analyzed the association of gene expression profiles to clinical outcome.

MATERIALS AND METHODS

Ten fresh samples of pleomorphic NOS sarcomas were evaluated histopathologically and by means of microarray analysis. Analysis of expression profiles was performed by clustering methods as well as by statistical analysis of primary vs recurrent tumors, irradiated vs nonirradiated tumors, tumors of patients above and below 60 years of age, male and female, and of tumors that developed metastatic or recurrent disease during the clinical course and those that did not.

RESULTS

Tumor clustering did not correlate to any histopathological or clinical finding. Detailed gene expression analysis showed a variety of genes whose upregulation (platelet-derived growth factor receptor alpha polypeptide, solute carrier family 39 member 14, solute carrier family 2 member 3, pleiotrophin, trophinin, pleckstrin and Sec7 domain containing 3, enolase 2, biglycan, SH3 and cysteine-rich domain, matrix metalloproteinases 16) and whose downregulation (tissue inhibitor of metalloproteinase 4, hairy/enhancer of split related with YRPW motif 2, protein tyrosine phosphatase receptor-type Z polypeptide 1, SH3 domain GRB2-like 2, microtubule-associated protein 7, potassium voltage-gated channel shaker-related subfamily member 1, RUN and FYVE domain containing 3, Sin3A-associated protein 18 kDa, proline-rich 4, calcium/calmodulin-dependent protein kinase ID, myeloid/lymphoid or mixed-lineage leukemia translocated to 3, insulin-like growth factor binding protein 5, nucleoside diphosphate-linked moiety X-type motif 9, NudC domain containing 3, imprinted in Prader-Willi syndrome, TAF6-like RNA polymerase II p300/CBP-associated factor 65 kDa, WD repeat and SOCS box-containing 2, adenosine diphosphate ribosylation factor 3, KRR1, proliferation-associated 2G4; CD36, complement component (3b/4b) receptor 1, solute carrier family 4 sodium bicarbonate cotransporter member 4, lipoprotein lipase (LPL), GATA binding protein 3, LPL, glutathione peroxidase 3, D: -aspartate oxidase, apolipoprotein E, sphingomyelin phosphodiesterase acid-like 3A) were associated with poor clinical outcome in terms of development of metastatic or recurrent disease.

CONCLUSIONS

The classification of these tumors may undergo further changes in the future. Gene expression profiling can provide additional information to categorize pleomorphic sarcoma (NOS) and reveal potential prognostic factors in this "entity."

[Long-term paratesticular leiomyosarcoma. Conceptual and literature review]

INTRODUCTION

To know the incidence and clinical and pathologic characteristics of the paratesticular leiomyosarcoma (LMS) with the contribution of a case of long evolution, studying the histopathologic criteria that must be valued for this type of tumours.

MATERIAL AND METHODS

A 73-year-old patient includes for study with scrotal tumour present left side for 30 months. Histopathologic and imunohistochemical study is realized. Of equal form there is realized a bibliographical search of this type of tumours and their different subtypes across Medline and of not index-linked search.

RESULTS

Our case is the second of greater evolution of international literature, first in greater of 60 years and one of those of smaller mitotic index (1 x 50 cga). Nevertheless, his atipia, tumorlike necrosis next to 50% of the injury and its pleomorphic properties, as well as his inmunophenotypic characterization corresponds with a well differentiated LMS, degree 1 (French Federation Cancer). We have found only 107 published cases of this type of sarcomas, of them 5 in our country, which gives to a profile of the low incidence of these tumours, that within sarcomas 1% do not reach. We included the clinical and pathologic profile of such.

CONCLUSIONS

The long evolution of a paratesticular tumour and the absence of metastasis does not exclude its malignancy. The low incident of the LMSs in this location, implies that a protocol of actuation validate for such does not exist. We considered of great importance, its creation on the part of urologist, oncologists, radiologists and pathologists like he took control of located in retroperitoneal cavity and deep soft tissues.

MFH revisited: outcome after surgical treatment of undifferentiated pleomorphic or not otherwise specified (NOS) sarcomas of the extremities -- an analysis of 140 patients

BACKGROUND

Undifferentiated pleomorphic sarcoma/NOS (not otherwise specified; former pleomorphic and storiform MFH) of the extremities is a common malignant soft tissue tumor in adults. The objective of this study is to determine prognostic factors for the outcome after surgical treatment with respect to the recent developments in classification.

METHODS

From 1996 to 2004, 140 undifferentiated pleomorphic sarcomas/NOS were identified out of 1,200 soft tissue sarcomas of the extremities that were treated at our institution and recorded in a prospective database. Overall survival (OS) and isolated local recurrence (ILR) were determined by Kaplan-Meier analysis. All tumors were retrospectively analyzed regarding prognostic factors of the disease, including patient's background (primary or recurrent), histological grade (G2/G3), adjuvant chemotherapy and radiotherapy, size (T1-2) and depth of the tumor, and surgical margins (R0, R1, R2).

RESULTS

In 123 patients, a wide resection was performed (limb-sparing surgery). In nine patients, an amputation was necessary. The overall 5-year survival rate was 72% (median follow up: 52 months). There was a significant difference between the group presenting with primary tumors (5-year survival: 84%, p < 0.05) and recurrent tumors (5-year survival: 62%, p < 0.05). Isolated local recurrence occurred in 36 patients.

CONCLUSIONS

In terms of OS and ILR, primary or recurrence, negative surgical margins, size and grading had a highly significant influence, whereas the site of surgery and adjuvant chemotherapy, adjuvant radiation and tumor depth did not. Prognosis for patients with undifferentiated pleomorphic sarcoma of the extremities depends predominantly on adequate wide resection of the primary tumor.

Malignant fibrous histiocytoma: between the past and the present

The precise nature and diagnostic concept of malignant fibrous histiocytoma (MFH) has been debated for years. Currently, a histiocytic lineage of the tumor cells is no longer favored. The nomenclature and classification of MFH and its subtypes have also been changed. The MFH pattern, especially that of storiform-pleomorphic variant, is viewed as a morphologic pattern shared by a number of sarcomas as well as by other nonsarcomas. Therefore, a diagnosis of MFH based solely on morphology is no longer acceptable and identification of a line of differentiation should be sought. A diagnosis of MFH should be made only for pleomorphic sarcomas in which no specific line of differentiation is discerned. Precise categorization of MFH-like tumors may require thorough sampling of the tumor and judicious use of immunohistochemistry and/or electron microscopy. Familiarity with the current terminology and classification of MFH and its subtypes is of paramount significance in the modern practice of pathology.

Undifferentiated pleomorphic sarcoma of the orbital region

Undifferentiated pleomorphic sarcoma (formerly known as malignant fibrous histiocytoma) has been established as an entity in the WHO-classification of soft tissue tumors since 2002. Before this the term "malignant fibrous histiocytoma" has been a collective term for soft tissue malignancies that had no distinct components and included most soft tissue sarcomas (40%). With the new classification they account for only about 5%, and tumors arising in the head and neck contribute only about 1-3% of all undifferentiated pleomorphic sarcomas. We report a rare case in which the orbital region was involved.

A case of primary malignant fibrous histiocytoma of the pancreas: CT and MRI findings

Primary malignant fibrous histiocytoma (MFH) of the pancreas is rare and a distinct clinical entity. We report a case of recurrence of pancreatic MFH with computed tomography (CT) and magnetic resonance imaging (MRI) findings. A 67-year-old man presented with a history of decreased body weight over the past 6 mo. Abdominal CT revealed a large, multilocular cystic mass in the head of the pancreas with obvious atrophy in the body and tail of the pancreas. After 6 mo postoperatively, MRI demonstrated a recurrent large mass in the primary area of the head of the pancreas. The lesion was heterogeneous, hypointense to the liver on T1-weighted imaging, and heterogeneously hyperintense to the liver with a hypointense area in the central part of the tumor on fat-saturated T2-weighted imaging. Contrast-enhanced T1-weighted imaging demonstrated a large multilocular cystic mass with a cystic wall, fibrous septa and enhancement of solid components. To the best of our knowledge, this is the first report on recurrence of primary MFH of the pancreas, and the first with MRI findings.

Identification of heterogeneity among soft tissue sarcomas by gene expression profiles from different tumors

The heterogeneity that soft tissue sarcomas (STS) exhibit in their clinical behavior, even within histological subtypes, complicates patient care. Histological appearance is determined by gene expression. Morphologic features are generally good predictors of biologic behavior, however, metastatic propensity, tumor growth, and response to chemotherapy may be determined by gene expression patterns that do not correlate well with morphology. One approach to identify heterogeneity is to search for genetic markers that correlate with differences in tumor behavior. Alternatively, subsets may be identified based on gene expression patterns alone, independent of knowledge of clinical outcome. We have reported gene expression patterns that distinguish two subgroups of clear cell renal carcinoma (ccRCC), and other gene expression patterns that distinguish heterogeneity of serous ovarian carcinoma (OVCA) and aggressive fibromatosis (AF). In this study, gene expression in 53 samples of STS and AF [including 16 malignant fibrous histiocytoma (MFH), 9 leiomyosarcoma, 12 liposarcoma, 4 synovial sarcoma, and 12 samples of AF] was determined at Gene Logic Inc. (Gaithersburg, MD) using Affymetrix GeneChip U_133 arrays containing approximately 40,000 genes/ESTs. Gene expression analysis was performed with the Gene Logic Genesis Enterprise System Software and Expressionist software. Hierarchical clustering of the STS using our three previously reported gene sets, each generated subgroups within the STS that for some subtypes correlated with histology, and also suggested the existence of subsets of MFH. All three gene sets also recognized the same two subsets of the fibromatosis samples that we had found in our earlier study of AF. These results suggest that these subgroups may have biological significance, and that these gene sets may be useful for sub-classification of STS. In addition, several genes that are targets of some anti-tumor drugs were found to be differentially expressed in particular subsets of STS.

Application of immunohistochemistry to soft tissue neoplasms

CONTEXT

Soft tissue tumors are composed of numerous and complex diagnostic entities. Because of this complexity and the recognition of an intermediate malignancy category including some tumors with a deceptively bland histologic appearance, soft tissue tumors may represent a major diagnostic challenge to the general practicing pathologist.

OBJECTIVE

To correctly diagnose soft tissue tumors with the ancillary use of immunohistochemistry.

DATA SOURCES

Review of the current literature with emphasis on those tumors for which immunohistochemistry has proven to be particularly useful.

CONCLUSIONS

Immunohistochemistry plays an important role in the diagnosis of soft tissue tumors. One of its major utilities is to correctly identify a tumor as being of mesenchymal or nonmesenchymal origin. Once mesenchymal origin has been established, histologic subtyping according to specific cell lineage may be achieved with the use of lineage-specific markers. Tumors of uncertain cell lineage and tumors with primitive small round cell morphology are often characterized by a unique immunohistochemical phenotype. In this group of tumors, immunohistochemistry is most widely applied and is of greatest value. Despite the rapid development of molecular genetic techniques, immunohistochemistry still remains the most important diagnostic tool in the diagnosis of soft tissue tumors aside from recognition of morphologic features and clinical correlation.

Oral undifferentiated high-grade pleomorphic sarcoma: report of a case

The current World Health Organization classification considers the existence of an undifferentiated unclassifiable category of pleomorphic sarcomas, defined as a group of pleomorphic high-grade sarcomas. Undifferentiated high-grade pleomorphic sarcoma represents about 5% of all soft tissue sarcomas in adults and occurs more commonly in the extremities. In the oral cavity, undifferentiated pleomorphic sarcoma is extremely rare. We report a case of undifferentiated high-grade pleomorphic sarcoma located in the floor of the mouth in a man 56 years old. Microscopically, spindle-shaped cells with accented pleomorphism arranged in a storiform pattern, several bizarre giant cells, and frequent atypical mitoses were observed. The tumor cells were positive only for vimentin, with focal positivity for CD68. The patient was treated by surgery and postoperative radiation therapy, and after 25 months, no recurrence was observed.

Casual discovery of a thoracic tumour showing histological features of undifferentiated pleomorphic sarcoma in a male Wistar laboratory rat

Sarcomas are neoplasms of mesenchymal origin, with a predominant cell population mimicking the organization of various soft tissues and/or bones. Previous categorizations also included the possibility of the presence of tissue macrophage-like (histiocytes) neoplasm cells, in a tumour described as malignant fibrous histiocytoma, but this group has been considered as a variety of undifferentiated pleomorphic sarcomas. Although this kind of malignancy is not rare in humans, only few cases have been reported in laboratory animals. We report an unusual single case of spontaneous tumour growth, detected by casual observation, in the left thoracic area of an 18-month-old male laboratory Wistar rat. Both this individual and his ancestors were not exposed to any known carcinogenic substance or radiation, thus suggesting the development of the neoplasm as a spontaneous event. The mass was extracted surgically under general anaesthesia, and slices were examined histologically and immunohistochemically, using photon microscopy. The pathologist reported the presence of a combination of fibroblasts and undifferentiated mesenchymal cells arranged in a storiform pattern. Immunohistochemistry was performed on the tissue using specific antibodies for several proliferation (Ki-67) and differentiation (S-100, CD-34, CD-68, pan-keratin, desmin and smooth muscle actin-SMA) markers. Positive reaction was observed for S-100, Ki-67, CD-68, desmin and SMA (limited) but not for CD-34 or cytokeratin.

Expression profiles in malignant fibrous histiocytomas: clues for differentiating 'spindle cell' and 'pleomorphic' subtypes

We analysed 21 samples of malignant fibrous histiocytoma (MFH) distinguished into the two principal morphological categories ('spindle cell' and the 'pleomorphic' subtypes). The aim of our study was to verify if a distinction between the two subclasses of MFH in terms of expression/activation of protein profiles could support and extend the morphological criteria. For this purpose, we carried out an immunohistochemical and immunoblotting analysis of proteins that could be relevant in sarcoma biology and potential diagnostic and therapeutical targets such as matrix metalloproteinases (MMPs) and molecules related to adhesive and proliferative properties. Our analysis revealed that MMP-1, MMP-9 expression and p27(kip1) cytoplasmic localisation can be considered valid parameters in the classification and potential explanation of the aggressive behaviour of this non-homogeneous group of MFH.

[A rare primary tumor of the mediastinum: pleomorphic liposarcoma]

Liposarcoma of the mediastinum is a rare tumor with various histologic features. We report a case of mediatinal pleomorphic liposarcoma in a 37-year-old man who complained of chest pain. Computed tomography showed an anterior expansive process within the mediastinum. Histological diagnosis was established by a trans-thoracic computed tomography guided core-needle biopsy. Despite a first cure of chemotherapy with gemcitabin/cisplatin, disease progression led to death 3 months after diagnosis. Mediastinal pleomorphic liposarcoma is an exceptional invading tumor affecting the middle-aged adult. This tumor, usually giant, becomes symptomatic by compression of mediastinal structures. Surgery is the best treatment when possible. The role of radiotherapy and chemotherapy are discussed. Prognosis depends both on the quality of resection and the grade malignancy.

Potential osteogenic differentiation of cisplatin-resistant rat malignant fibrous histiocytoma-derived cell lines

Histological modulations in tumor cells treated with anti-cancer drugs have been reported. The histogenesis of malignant fibrous histiocytoma (MFH) remains elusive. To investigate cellular characteristics and alterations, therefore, we derived cisplatin-resistant MFH cell lines (MT-PR and MT-10R) from MT-P and MT-10, respectively, and compared them with MT-10, a non-cisplatin-resistant MFH line (MT-10 was isolated as a clone cell line from MT-P, and MT-P was originally established from a rat spontaneous MFH). Immunohistochemically, MT-10 reacted to vimentin, alpha-smooth muscle actin (a marker of myofibroblasts), ED1/ED2 (rat macrophage/histiocyte-specific antibodies), and A3 (rat MFH-specific antibody) in varying degrees, indicating that MFH cells have features of both fibroblasts and histiocytes. However, MT-10R and MT-PR reduced ED1-positive cell numbers. MT-10 developed tumors of a storiform pattern, while MT-10R and MT-PR tumors comprise round or polygonal cells arranged in a compact sheet. Additionally, MT-PR tumors included ossifying areas. MT-10R and MT-PR, and their tumors showed a reaction to alkaline phosphatase (ALP), a marker of osteoblasts. RT-PCR revealed that mRNAs of bone morphogenetic protein (BMP)-2, BMP-6 and osteopontin were significantly increased in MT-10R and MT-PR tumors. Neoplastic cells in these tumors were immunoreactive to BMP-2 and BMP-6, while MT-10 tumors were not. Cisplatin-resistant MFH cells had potential to differentiate into osteogenic tissues by producing osteogenic factors, suggesting that MFH histology may be altered under anti-cancer drug treatments. Recently, cancer differentiation-based therapy, that could be induced by anti-cancer drugs, has been implied. MT-10R and MT-PR become useful experimental systems for studies on cellular differentiation provoked by anti-cancer drugs.