SUBCUTANEOUS PANNICULITIS-LIKE T-CELL LYMPHOMA; This spontaneous report was received from literature.  The subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare subtype of primary cutaneous T-cell lymphoma defined by neoplastic a/b T-cell infiltration of the subcutaneous fat, mimicking an inflammatory panniculitis. SPTCL makes up only 1% of primary cutaneous lymphomas.Given the paucity of cases reported in the literature, little is known about the precise epidemiology, risk factors, and causative factors in the development of SPTCL. We describe a young woman who developed SPTCL at the injection site of a recent COVID-19 vaccination. This report concerned a 28 year old female of an unspecified race and ethnicity. The patient's height and weight were not reported. The patient was previously healthy. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin and batch number were not reported, expiry: Unknown) dose, start therapy date were not reported, primary dose, 1 total administered to the upper arm for covid-19 prophylaxis. The batch number was not reported and has been requested. No concomitant medications were reported. It was reported that, few days later vaccination, on an unspecified date the patient developed a nodule at the injection site. Over the next 3 months, the nodule progressively enlarged to become a plaque with associated pain, warmth, and paresthesias. She also developed cervical and left axillary lymphadenopathy, intermittent fevers, fatigue and unintentional weight loss. It was mentioned that the Presumptive treatment for cellulitis with several courses of oral antibiotics was ineffective. The physical examination revealed a large erythematous indurated plaque on the upper arm and cervical and axillary lymphadenopathy. The patient presented with fever (38 degrees Celsius), mild anemia, leukopenia and neutropenia. Punch biopsies revealed a lobular panniculitis with a subcutaneous infiltrate of atypical lymphocytes rimming adipocytes with fibrinoid necrosis and large histiocytes containing apoptotic debris. The atypical lymphocytes were CD3+, CD7+, CD8+, perforin+, T-cell receptor, TCR-beta+, TCR-delta-, CD4-, CD56-, EBER-, ISH- and CD30- with an elevated proliferation index highlighted by Ki-67. Following extraction of genomic DNA, the TCR gamma gene was amplified using a multiplex polymerase chain reaction master mix according to author. Polymerase chain reaction products were resolved by capillary electrophoresis. Molecular genetic analysis for TCR gamma gene rearrangement revealed a polyclonal distribution, although with 2 suspicious peaks, one at 187 bp of master mix I and the second at 220 bp of master mix I. According to the Regulatory Authority classification, the clinical and histopathologic findings were consistent with SPTCL (subcutaneous panniculitis-like t-cell lymphoma). It was also reported that the patient developed tender cervical, submandibular, right axillary, and right popliteal lymphadenopathy with persistence of the subcutaneous plaque and new subcutaneous nodules on both arms. Positron emission tomography (computed tomography (PET-CT) scan) showed multifocal subcutaneous lesions in the right forearm (standardized uptake value [SUV] max: 10.34), left arm and axilla (SUV max: 10.26), jaw (SUV max: 11.9), right supraclavicular region (SUV max: 8.88), back (SUV max:3.72), pelvis (SUV max: 6.7), right calf (SUV max:5.27), and left knee (SUV max: 3.66). Patchy fluorodeoxyglucose uptake was also seen in the tibias. The spleen was enlarged to 13.7 cm with increased fluorodeoxyglucose uptake relative to the liver. The treatment was initiated with cyclosporine 5 mg/ kg/day. Since the patient only showed modest improvement after 2 weeks, prednisone 50 mg daily was added. Three weeks after combination therapy, the anemia, leukopenia, and neutropenia resolved and by 6 weeks, the patient's fatigue, the subcutaneous nodules, and the lymphadenopathy had nearly resolved. The original plaque at the site of vaccination resolved with prominent atrophy. PETCT scan (Positron emission tomography) at 3-month follow-up showed improvement or resolution of all widespread subcutaneous lesions, no new lesions, and decreased splenomegaly. The prednisone was tapered over 4 months, and she has completed 8 months of a 12-month course of cyclosporine therapy. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of subcutaneous panniculitis-like t-cell lymphoma was not reported. It was concluded that due to the rarity of SPTCL, there are few data to characterize the demographic risk factors, comorbid medical conditions, and inciting factors associated with the disease. The median age of presentation is 36 years, females are twice as likely to be affected as males, and up to 20% of patients have a co-existing autoimmune disease. In this manuscript, we present a case of SPTCL that developed following the Ad26 viral vector-based COVID-19 vaccine (Janssen Pharmaceuticals). Although causation cannot be established in this single case, this case supports the understanding that certain immunologic triggers, such as a modified adenovirus vaccine, may contribute to the development or exacerbation of SPTCL. In this case, PET-CT scan showed diffuse subcutaneous, lymph node, and splenic enhancement, representing relatively aggressive disease for this diagnosis. However, consistent with SPTCL and in contrast to primary cutaneous g/d T-cell lymphoma, her disease responded promptly to conservative treatment. In the case presented, cyclosporine and prednisone therapy resulted in significant improvement with resolution of induration and erythema, systemic symptoms, and subcutaneous nodules. This case adds to accumulating data favoring the use of immunosuppressive agents as first-line treatment for SPTCL rather than chemotherapy. This report was serious (Other Medically Important Condition).; Sender's Comments: V0: 20220950916-covid-19 vaccine ad26.cov2.s-Subcutaneous panniculitis-like T-cell lymphoma. The event(s) shows an incompatible temporal relationship. Therefore, this event(s) is considered not related.