| Pathway/Gene | Type of Alteration | Functional Consequence | Frequency in GCTs | Therapeutic Relevance |
|---|---|---|---|---|
| **ATP6AP1** | Recurrent somatic loss-of-function; frameshift variants reported | Impairs V-ATPase accessory function, disrupts endosomal/lysosomal acidification, promotes lysosomal/autophagosomal granule accumulation characteristic of GCT | Part of the recurrent V-ATPase gene set present in ~72% of GCTs; individual-gene frequency varies (pqac-00000002, pqac-00000028, pqac-00000032) | Core diagnostic molecular feature; mechanistic rationale for targeting downstream RTK signaling, especially pazopanib-sensitive kinase networks (pqac-00000029, pqac-00000017) |
| **ATP6AP2** | Recurrent somatic loss-of-function | V-ATPase dysfunction with abnormal vesicle acidification; enhances oncogenic signaling downstream of lysosomal stress | Part of the recurrent V-ATPase gene set present in ~72% of GCTs (pqac-00000003, pqac-00000028, pqac-00000029) | Supports targeted therapy rationale via downstream PDGFR-β/SFK/STAT5 activation; also useful diagnostically (pqac-00000029, pqac-00000016) |
| **ATP6V0C** | Recurrent inactivating/loss-of-function mutation | Disrupts V-ATPase proton pump function and lysosomal homeostasis | Included among recurrent V-ATPase alterations in up to ~72% of GCTs (pqac-00000004, pqac-00000026, pqac-00000032) | Supports pathway-based targeting of consequences of V-ATPase dysfunction rather than direct current gene-specific therapy (pqac-00000026, pqac-00000030) |
| **PDGFR-β** | Increased phosphorylation/activation downstream of V-ATPase loss | Promotes oncogenic signaling, proliferation, and survival in Schwann-lineage tumor cells | Activation described as a downstream event in V-ATPase-mutant GCTs; prevalence not independently quantified (pqac-00000026, pqac-00000028, pqac-00000029) | Major proposed kinase target; likely contributor to pazopanib activity in advanced/malignant GCT (pqac-00000002, pqac-00000027) |
| **SFK / Src family kinases** | Increased phosphorylation/activation | Enhances pro-oncogenic signaling downstream of ATP6AP1/2 loss | Activation described in V-ATPase-altered GCTs; exact frequency not separately reported (pqac-00000026, pqac-00000027, pqac-00000029) | Provides rationale for kinase-directed therapy; dasatinib has been tried clinically but reported ineffective in isolated cases (pqac-00000016, pqac-00000022) |
| **STAT5a/b** | Increased signaling/phosphorylation | Supports proliferation and survival signaling downstream of lysosomal/V-ATPase dysfunction | Activation reported mechanistically; exact frequency not separately reported (pqac-00000026, pqac-00000027, pqac-00000028) | Potential downstream vulnerability, though no established STAT5-targeted regimen exists for GCT (pqac-00000026, pqac-00000029) |
| **PI3K/AKT/mTOR pathway** | Pathway activation, especially in malignant GCT | Promotes cell survival, proliferation, motility, and aggressive behavior | Implicated particularly in malignant GCT; population frequency not established (pqac-00000026) | Clinical relevance supported by a reported PI3K inhibitor achieving ~9 months disease control in one advanced case (pqac-00000016, pqac-00000021) |
| **TP53** | Alterations in malignant GCT | Associated with malignant progression and biologic aggressiveness | Reported in malignant GCTs; uncommon in benign conventional GCT; exact frequency not established (pqac-00000026) | May help distinguish malignant biology; no GCT-specific targeted therapy established (pqac-00000026) |
| **PIK3CA** | Alterations in malignant GCT | Activates PI3K signaling and may contribute to progression/aggressiveness | Reported in malignant GCTs; exact frequency not established (pqac-00000026) | Supports consideration of PI3K-pathway inhibition in selected advanced cases (pqac-00000016, pqac-00000021, pqac-00000026) |
| **TGFβ pathway (TGFBR1/TGFBR2)** | Mutations/alterations | Suggests additional pathway dysregulation contributing to tumorigenesis | Reported as additional alterations; frequency not established (pqac-00000026) | Currently mainly biologic/interpretive relevance; no standard targeted use in GCT (pqac-00000026) |
| **MAPK pathway (including MAP3K15)** | Mutations/alterations | May contribute to tumorigenesis and overlap with syndromic RAS-MAPK biology | Reported as additional alterations; frequency not established (pqac-00000026, pqac-00000027) | Supports exploration of MAPK-directed combinations; MEK-inhibitor combinations with pazopanib have been discussed experimentally in sarcoma contexts (pqac-00000020, pqac-00000021) |


*Table: This table summarizes the main genetic alterations and signaling pathways implicated in granular cell tumor pathogenesis, with their functional effects and therapeutic implications. It is useful for linking recurrent V-ATPase defects to downstream targetable signaling in malignant or advanced disease.*