Distinct coexisting pathologies of oral malignant peripheral nerve sheath tumor with melanin pigmentation and indolent small lymphocytic lymphoma

Spindle cell malignancies of the oral cavity are uncommon and pose considerable diagnostic challenges due to overlapping histomorphology and immunohistochemical features. Malignant peripheral nerve sheath tumor (MPNST) with heterologous differentiation is particularly rare. Moreover, its coexistence with a synchronous hematological malignancy such as small cell lymphoma (SLL) is exceedingly unusual. A male 62 year, presented with a progressively enlarging, pigmented, ulcero-proliferative painless mass over the right upper alveolus extending to the hard palate. Imaging revealed a heterogeneously enhancing mass with cervical lymphadenopathy. Initial punch biopsy suggested fibroma/low-grade spindle cell neoplasm, but frozen biopsy raised the suspicion of malignant melanoma or spindle cell sarcoma. The patient underwent right upper alveolectomy with bilateral modified radical neck nodal dissection (MRND). Histopathological evaluation revealed spindle cell morphology with heterologous melanin pigmentation, favoring MPNST with dedifferentiation. Extensive nodal dissection (134 lymph nodes) revealed small cell lymphoma (SLL, stage I) in a few nodes. Immunohistochemistry (IHC) confirmed a dual primary malignancy -MPNST with rhabdomyoblastic and smooth muscle differentiation coexisting with SLL. This case illustrates the uniqueness of synchronous dual malignancies involving MPNST and SLL, a combination rarely documented in the oral cavity. The diagnostic challenge lay in distinguishing spindle cell malignancies with overlapping features, requiring multidisciplinary approach and IHC testing. The patient was managed with complete surgical excision and adjuvant radiotherapy (60 Gy/30 Fractions), with no evidence of systemic lymphoma or metastasis. for six weeks. At two yrs follow up, the patient remained disease free, highlighting the favorable outcome despite the complexity of diagnosis.