Inclusion Criteria:

1. Male or female, 18 years old or older.

2. Histologically or cytologically confirmed diagnosis of a solid tumor (RCC, HCC, or
colorectal cancer).

3. Participants are planning to initiate treatment with either sorafenib or regorafenib
as a single chemotherapeutic agent

4. Able to swallow and retain oral medication and does not have any clinically relevant,
active gastrointestinal disease or other condition that may significantly alter
absorption, distribution, metabolism, or excretion of drugs.

5. Be able to provide written informed consent.

Exclusion Criteria

1. Patients who are or will be receiving other chemotherapeutic or molecularly targeted
agents in addition to sorafenib or regorafenib

2. Concurrent moderate or severe chronic inflammatory skin condition (eczema, psoriasis)

3. Concurrent blistering skin disorder of any severity (such as pemphigus, bullous
pemphigoid)

4. Connective tissue disorders with skin involvement (systemic lupus erythematosus,
scleroderma, dermatomyositis, etc.)

5. Patients manifesting an allergic skin reaction (such as urticaria) or skin reaction
as a complication of prior chemotherapy

6. Patients with skin lesions of infectious or non-infectious cause, precluding skin
biopsy

7. Patients not willing to undergo skin biopsy

8. Patients who are pregnant or planning to become pregnant during their participation
in the study.

9. Chemotherapy, targeted therapy, or biological therapy within two weeks of start of
treatment.

10. Ability to give informed consent is compromised by cognitive and/or decisional
impairment.