Lymphomatoid papulosis (LyP); Lymphomatoid reaction; This literature-non-study case was reported in a literature article and describes the occurrence of LYMPHOMATOID PAPULOSIS (Lymphomatoid papulosis (LyP)) and PSEUDOLYMPHOMA (Lymphomatoid reaction) in a 53-year-old male patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.   LITERATURE REFERENCE:     Concurrent medical conditions included Hand eczema (Since teenage years.).   On an unknown date, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, received second dose of mRNA-1273 (Spikevax) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced LYMPHOMATOID PAPULOSIS (Lymphomatoid papulosis (LyP)) (seriousness criterion medically significant). an unknown date, the patient experienced PSEUDOLYMPHOMA (Lymphomatoid reaction) (seriousness criterion medically significant). The patient was treated with PREDNISONE (oral) at an unspecified dose and frequency; VALACYCLOVIR [VALACICLOVIR] at an unspecified dose and frequency and DOXYCYCLINE at an unspecified dose and frequency. At the time of the report, LYMPHOMATOID PAPULOSIS (Lymphomatoid papulosis (LyP)) and PSEUDOLYMPHOMA (Lymphomatoid reaction) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Biopsy: The left lateral neck and central neck specimens both showed an atypical epidermotropic T-cell infiltrate composed of intermediate to large-sized T-cells that expressed CD3 (a subset showed weak CD3 expression) and co-expressed CD4 and TIA1 CD2, CD5, and CD7 were diminished in expression. Enlarged atypical T-cells with some epidermotropism that expressed CD3 (original x100), CD4, TIA-1 and limited CD30 expression by the atypical T-cells in the initial biopsies. The findings were favored to represent a lymphomatoid reaction though a CD30 positive T-cell lymphoproliferative disorder such as lymphomatoid papulosis (LyP) remains in the differential diagnosis.. On an unknown date, Biopsy skin: The left shoulder biopsy specimen demonstrated aggregates of large, atypical T-cells with epidermotropism that expressed CD3  and CD4 and showed loss of CD5 and CD7. CD30 highlights a subset of cells.. On an unknown date, Flow cytometry: Flow cytometry performed on peripheral blood was negative for involvement.. On an unknown date, Fluorescent in situ hybridisation: (Negative) In situ hybridization for EBER was negative.. On an unknown date, Full blood count: Complete blood counts with differential and peripheral blood flow cytometry did not reveal evidence of systemic disease.. On an unknown date, Polymerase chain reaction: Revealed clonal rearrangements in the genes encoding T-cell receptor ? (TRG) and T-cell receptor ß (TRB) with matching base pair peaks in the lateral neck, central neck, and left anterior shoulder biopsy specimens..     For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   No concomitant medication was reported.  The patient was presented with a papulonodular eruption on his head and the front of his neck approximately one week after receiving first dose of the Moderna COVID-19 vaccine. After the second dose, the rash worsened significantly and was intensely pruritic However, the patient did not experience systemic symptoms at any time.   The papules/pustules would grow, drain serous fluid, and then regress. The rash persisted despite a two-week course of oral prednisone. It was progressively spread across the chest, back, axillae, and inguinal regions. Valacyclovir, doxycycline, and hydroxyzine were attempted without success.  Positron emission tomography-computed tomography was not performed due to lack of insurance coverage.  The rash improved significantly without additional intervention with only residual hyperpigmentation and hyperpigmented scars remaining and the patient had remained disease free for the past 12 months. Given the close association with vaccination and complete resolution.   This literature non-study case concerns a 53-year-old male patient, with relevant medical condition of eczema, who experienced the unexpected and serious (due to medically significant) events of Lymphomatoid papulosis and Pseudolymphoma. Patient presented with a papulonodular eruption on his head and the front of his neck approximately one week after receiving his first dose of mRNA-1273 vaccine. After the second dose, the rash worsened significantly and was intensely pruritic. However, the patient did not experience systemic symptoms at any time. Complete blood counts with differential and peripheral blood flow cytometry did not reveal evidence of systemic disease. The papules/pustules would grow, drain serous fluid, and then regress. The rash persisted despite a two-week course of oral prednisone. It progressively spread across the chest, back, axillae, and inguinal regions. Valacyclovir, doxycycline, and hydroxyzine were attempted without success. Multiple punch biopsies were performed. The left lateral neck and central neck specimens both showed an atypical epidermotropic T-cell infiltrate composed of intermediate- to large-sized T-cells that expressed CD3 and co-expressed CD4 and TIA1. CD2, CD5, and CD7 were diminished in expression. In situ hybridization for Epstein-Barr encoding region was negative. CD30 marked a subset of cells. A subsequent skin biopsy specimen from the left anterior shoulder showed a similar atypical T-cell infiltrate with epidermotropism and a similar immunophenotype with more robust CD30 expression. Polymerase chain reaction (PCR) revealed clonal rearrangements in the genes encoding T-cell receptor ? (TRG) and T-cell receptor ß (TRB) with matching base pair peaks in the lateral neck, central neck, and left anterior shoulder biopsy specimens. The rash improved significantly without additional intervention with only residual hyperpigmentation and hyperpigmented scars remaining, and the patient has remained disease free for the past 12 months. Given the close association with vaccination, complete resolution, and limited CD30 expression by the atypical T-cells in the initial biopsies, the findings were favored to represent a lymphomatoid reaction, though a CD30- positive T-cell lymphoproliferative disorder such as lymphomatoid papulosis remains in the differential diagnosis. Immune stimulation following exposure to SARS-Cov-2 protein(s) in vaccine or infection may facilitate the development of a lymphoma or lymphoproliferative disorder in susceptible individuals (in this case, patient´s eczema). The benefit-risk relationship of mRNA-1273 is not affected by this report.  Most recent FOLLOW-UP information incorporated above includes: On 07-Dec-2022: Live follow-up received by safety on 08-Dec-2022 has Email with FTA and contains significant information. Reporter information, literature information, medical history, lab data, treatment medication and event information were updated.; Sender's Comments: This literature non-study case concerns a 53-year-old male patient, with relevant medical condition of eczema, who experienced the unexpected and serious (due to medically significant) events of Lymphomatoid papulosis and Pseudolymphoma. Patient presented with a papulonodular eruption on his head and the front of his neck approximately one week after receiving his first dose of mRNA-1273 vaccine. After the second dose, the rash worsened significantly and was intensely pruritic. However, the patient did not experience systemic symptoms at any time. Complete blood counts with differential and peripheral blood flow cytometry did not reveal evidence of systemic disease. The papules/pustules would grow, drain serous fluid, and then regress. The rash persisted despite a two-week course of oral prednisone. It progressively spread across the chest, back, axillae, and inguinal regions. Valacyclovir, doxycycline, and hydroxyzine were attempted without success. Multiple punch biopsies were performed. The left lateral neck and central neck specimens both showed an atypical epidermotropic T-cell infiltrate composed of intermediate- to large-sized T-cells that expressed CD3 and co-expressed CD4 and TIA1. CD2, CD5, and CD7 were diminished in expression. In situ hybridization for Epstein-Barr encoding region was negative. CD30 marked a subset of cells. A subsequent skin biopsy specimen from the left anterior shoulder showed a similar atypical T-cell infiltrate with epidermotropism and a similar immunophenotype with more robust CD30 expression. Polymerase chain reaction (PCR) revealed clonal rearrangements in the genes encoding T-cell receptor ? (TRG) and T-cell receptor ß (TRB) with matching base pair peaks in the lateral neck, central neck, and left anterior shoulder biopsy specimens. The rash improved significantly without additional intervention with only residual hyperpigmentation and hyperpigmented scars remaining, and the patient has remained disease free for the past 12 months. Given the close association with vaccination, complete resolution, and limited CD30 expression by the atypical T-cells in the initial biopsies, the findings were favored to represent a lymphomatoid reaction, though a CD30- positive T-cell lymphoproliferative disorder such as lymphomatoid papulosis remains in the differential diagnosis. Immune stimulation following exposure to SARS-Cov-2 protein(s) in vaccine or infection may facilitate the development of a lymphoma or lymphoproliferative disorder in susceptible individuals (in this case, patient´s eczema). The benefit-risk relationship of mRNA-1273 is not affected by this report.