Adult fibrosarcoma: From clinical challenges to cutting-edge innovations

Histologic architecture

Adult fibrosarcoma is a diagnosis of exclusion and demonstrates a hallmark histologic architecture, with monomorphic spindle-shaped fibroblasts aligned in a distinctive herringbone pattern embedded within a variably collagenous matrix. Tumor cells possess scant cytoplasm, elongated hyperchromatic nuclei, and exhibit frequent mitotic activity, particularly pronounced in higher-grade lesions. Despite this proliferative profile, nuclear pleomorphism remains limited, a feature that aids in distinguishing fibrosarcoma from other aggressive spindle cell sarcomas [3].

Molecular alterations

Adult fibrosarcoma is marked by chromosomal instability, often presenting with aneuploidy and recurrent NTRK3 gene fusions (STRN1-NTRK3 or STRN3-NTRK3), which are actionable targets for tyrosine kinase inhibitors. Critical amplifications in chromosome 12q (especially 12q14–q15 and 12q21) and gains in regions like 1p21, 4q31.3, 7p21, and Xp22.1–p22.2 are common and tied to poor prognosis [4]. These molecular alterations help differentiate fibrosarcoma from other spindle cell neoplasms and inform potential targeted treatment strategies. TP53, CDKN2A, and RB1 are the most frequently altered genes in soft tissue sarcomas, with TP53 mutations and CDKN2A/RB1 copy number losses playing pivotal roles in tumor progression and prognosis. Among these, CDKN2A loss stands out for its strong association with early recurrence and poor outcomes, especially in fibrosarcoma and MPNST [5].

Tumor-host neurobiology

Adult fibrosarcoma is a locally aggressive malignancy with a high propensity for hematogenous spread, particularly in high-grade variants that exhibit rapid proliferation, necrosis, and recurrence. Adult fibrosarcoma leverages a sophisticated neurobiological strategy to reshape systemic homeostasis in favor of tumor growth. Beyond evading immune surveillance, it actively manipulates neuroendocrine pathways through the secretion of cytokines, catecholamines, serotonin, melatonin, glucocorticoids, and other mediators. These tumor-derived signals target key regulatory centers i.e., the hypothalamus, pituitary, adrenal glands, and thyroid and disrupts host balance via feedback mechanisms that support tumor expansion [6].

Simultaneously, fibrosarcoma engages in reciprocal signaling with autonomic and sensory nerves within the tumor microenvironment. This bidirectional crosstalk fosters neural infiltration and neoaxonogenesis, while neurotransmitters released from infiltrating nerves drive tumor proliferation, angiogenesis, and immune suppression. The result is a remodeled tumor niche and systemic environment primed for cancer dominance. Extending beyond local effects, this interaction impacts brain function, circadian rhythm, stress response, and immune dynamics mirroring mechanisms seen in other cancers that hijack neuroimmune and neuroendocrine systems [6, 7].

Collectively, adult fibrosarcoma exemplifies how solid tumors can orchestrate a multi-layered physiological reprogramming, warranting therapeutic strategies that address both tumor-intrinsic mechanisms and host regulatory networks.

Imaging features

MRI reveals well-defined lesions with hypointense signals on T1WI and heterogeneous intensity on T2WI, which are more prominent on fat-saturated sequences. CT imaging shows iso-attenuating masses with band-like areas, resembling muscle tissue. Post-contrast scans with Gd-DTPA highlight characteristic enhancement patterns, including heterogeneous peripheral enhancement and a spoke-wheel-like configuration, strongly indicative of adult fibrosarcoma [8]. PET-CT assists with the metastatic work-up.

Immunohistochemistry and sub-types

Immunohistochemically, the tumor exhibits diffuse vimentin positivity and a high Ki-67 proliferative index, consistent with a mesenchymal origin and active mitosis. The absence of markers such as S100, cytokeratin, and smooth muscle actin helps exclude other spindle cell neoplasms, supporting a fibroblastic lineage. Advanced immunohistochemical and molecular techniques are essential for accurately classifying fibrosarcoma subtypes, which often display overlapping morphologic and genetic features.

Key subtypes include Low-Grade Fibromyxoid Sarcoma, Sclerosing Epitheloid Fibrosarcoma, and Myxofibrosarcoma. Additionally, differential diagnosis should carefully consider spindle-cell neoplasms such as Solitary Fibrous Tumor, Monophasic Fibrous Synovial Sarcoma, Epitheloid Sarcoma, spindle cell variants of Angiosarcoma, Malignant Peripheral Nerve Sheath Tumor, and Aggressive Fibromatosis [1, 9].

Grading and staging systems

AJCC Grading helps stage the disease and predict tumor behavior and guide treatment. The FNCLCC system assigns scores based on differentiation, mitotic count and tumour necrosis where each component is scored from 1–3. Total of these scores is further divided into grades as follows:

• Grade 1 (G1): Score 2–3 → Low-grade, slower growth and spread.

• Grade 2 (G2): Score 4–5 → Intermediate-grade.

• Grade 3 (G3): Score 6–8 → High-grade, aggressive behavior.

• Grade X: Grade cannot be assessed.

AJCC Staging is determined by size of the tumour (T), nodal spread, grade determined by FNCLCC and metastasis [10]. Staging is done as shown in Table 1.

Treatment strategies

The surgical approach for adult fibrosarcoma is guided by the tumor’s location, size, and grade. Whenever feasible, wide resection with R0 margins is performed to achieve complete tumor removal. For tumors exceeding 5 cm, deeply situated, or classified as high-grade, adjuvant radiation therapy is recommended to minimize recurrence risk [11].

Though, adult fibrosarcoma is chemoresistant, chemotherapy can be administered in the neo-adjuvant setting in high-grade or metastatic fibrosarcomas, with commonly used agents including doxorubicin, ifosfamide, gemcitabine, and paclitaxel [12, 13]. Stage-wise management of Adult Fibrosarcoma is briefly outlined in Table 2.

Advances in treatment

Immune checkpoint inhibitors like pembrolizumab and nivolumab enhance immune system activity by targeting the PD-1/PD-L1 pathway, potentially improving treatment response [14].

In tumors harboring NTRK3 fusions (e.g., STRN1-NTRK3), larotrectinib or entrectinib can achieve durable responses and are considered in molecular-guided approaches [15].

Advances in targeting matrix metalloproteinases (MMPs) and tumor microenvironment interactions have opened new avenues for fibrosarcoma treatment, focusing on selective inhibition and localized therapeutic strategies. Innovations like TIMP-1-GPI application and homotrimeric collagen degradation show promise in enhancing chemosensitivity and overcoming drug resistance, potentially improving patient outcomes [2].

Although not yet standard in fibrosarcoma, further targeting neural-tumor interactions (e.g., anti-NGF therapies, β-blockers, Trk inhibitors) is a growing area of interest in oncology and represent a promising frontier in cancer treatment, offering novel avenues to disrupt tumor-supportive neural signaling and reshape the tumor microenvironment [7].