PMC8116704_01
TAMA. Skin and mucosal lesions photographed (A) at the onset of chemotherapy, (B) after six cycles of systemic treatment and (C) after three months of prednisone therapy.
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On admission, she reported a six-month history of poor appetite, weight loss of 12 kg (24% of initial body weight), generalized fatigue, muscle weakness, oral cavity lesions resembling candidiasis that persist despite antifungal therapy, erythematous scaly papules affecting skin surrounding her nose, mouth and buttocks, as well as the distal parts of the upper extremities and palms, with concomitant degeneration of the finger nail plates ( Figure 1A ). During the systemic treatment, symptoms mitigated and patient's condition gradually improved, however with no signs of reduction of mucocutaneous lesions ( Figure 1B ). Unfortunately, neither skin nor mucosal lesions resolved after three months of low-dose prednisone therapy ( Figure 1C ); no other anti-cancer treatment was administered and dosing of 0.5 mg/kg a day was not escalated due to poor tolerance. Detailed timeline on the patient's diagnostic process and treatment was presented in the  Supplementary Figure 1 .
Thymoma. Computer tomography imaging showing maximal tumor dimensions (upper row) and infiltration on VCS (bottom row): (A) prior systemic treatment (64 x 30 x 76 mm); (B) after completion of chemotherapy (51 x 26 x 70 mm); (C) prior corticosteroids implementation (65x63x75mm); (D) after three months of corticosteroid therapy (30x17mm).
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Cooperative Oncology Group (ECOG) was assessed as 4, mostly due to severe muscle weakness. Computed tomography (CT) revealed a locally advanced tumor (64 x 30 x 76 mm) in the upper part of the anterior mediastinum with suspected infiltration of superior vena cava (VCS); no signs of distant metastases nor lymph node involvement were observed ( Figure 2A ). A CT scan after six cycles of chemotherapy showed that the longest diameter of the tumor slightly decreased from 76 mm to 70 mm ( Figure 2B ). Quite unexpectedly, routine follow-up CT scan revealed good partial response (PR) of the upper-mediastinal mass, according to RECIST 1.1 criteria, with its measurements decreasing substantially to 30 mm from 75 mm prior to corticosteroid therapy, and the disappearance of VCS infiltration ( Figures 2C, D  ).
TAMA. HE and immunostaining of the skin (A) and oral mucosa (B) samples in magnification.
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CD4+>CD8+ at a ratio of 1.5-2:0, incidental CD30+), and focal destruction of skin appendages ( Figure 3A ) despite the lack of HSCT or organ transplantation in the patient's past medical history. Correspondingly, GvHD-like changes were also reported in the oral mucosa sample: intensive T-cell infiltration (CD3+, CD4+>CD8+ at a lower ratio than in skin sample, incidental B-cell lymphocytes), basal layer destruction, acanthosis, hyperkeratosis ( Figure 3B ). Blood serum evaluation was negative for RF, anti-CCP, anti-Ro, anti-La and anti-dsDNA and weakly positive for anti-Sm antibodies.