Inclusion Criteria:  Group A: Criteria 1-5 Group B: Criteria 2-5 Group C: Criteria 2-6  Small fiber neuropathy (after clinical examination or QST or skin biopsy findings) Legal age Written declaration of consent Persons who are legally competent and mentally capable of following the instructions of the staff Sufficient affinity for independent handling of the technology used (PainWatch incl. the corresponding apps) for daily digital pain recording Imminent initiation of neurotoxic chemotherapy in cancer with solid tumors (preferably of the gastrointestinal tract) There are no plans for follow-up recruitment in case no neuropathy develops after chemo.  Exclusion Criteria:  For all Groups:  Persons who are accommodated in an institution by order of the authorities or courts Persons who are in a dependent or employment relationship with the auditor For test persons: Exclusion, if they carry a known pain-relevant genetic variant/mutation or suffer from a chronic pain disorder analogous to migraine or chronic back pain.