Dear Editor, A cutaneous horn is a protrusion from the skin consisting of cornified material organized in the shape of a horn. It can hide a broad spectrum of pathology at its base; this may be benign, premalignant, or malignant. Large cutaneous horns, particularly giant horns, are considered to be commonly derived from malignant bases.[1] Risk factors of underlying malignancy include advanced age, male sex, large base or low height-to-base ratio and location on sun-exposed areas.[2] A 45-year-old female, having disseminated discoid lupus erythematosus (DLE) for the last seven years, presented with an asymptomatic brownish-black growth protruding from her lower lip since the last one month. Clinical examination revealed a solitary, well circumscribed, brownish-black, horn-like, hard lesion, measuring 2.7 × 2.0 cm, arising over the depigmented lesion of DLE over the lower lip [Figure 1]. There was no history of previous trauma, spontaneous bleeding, or ulceration. She was a non-smoker with good oral hygiene and no history of significant sunlight exposure during her routine daily activities. There were no enlarged regional lymph nodes and she was in good health with no systemic symptoms. An excisional biopsy was performed. Histopathology revealed nests of neoplastic squamous cells with pleomorphic, hyperchromatic, and vesicular nuclei. Prominent nucleoli and mitosis were also seen. Keratinization and keratin pearl formation were present [Figures 2a and b]. Based on these findings, a diagnosis of moderately differentiated keratinizing squamous cell carcinoma with cutaneous horn superimposed over DLE was made. Routine investigations revealed anemia and leucopenia (Hb-9 gm% and TLC-3600/mm3). Antinuclear antibody test was strongly positive in dilutions of 1:320 to 1:1000, with a nuclear speckled pattern, and anti-double-stranded DNA was positive in dilutions of 1:100 to 1:320. Other blood tests and biochemical tests were normal. The patient’s postoperative recovery period was uneventful, with complete healing occurring in seven days. However, when the patient was seen after two months, a minor recurrence of the growth was observed over the same site [Figure 3a]. She was treated with topical 5-fluorouracil 1% cream daily with complete regression of the lesion in two weeks’ duration [Figure 3b]. She has been maintaining the remission for the last three months.Figure 1: Cutaneous horn arising on a depigmented lesion of DLE over the lower lipFigure 2: (a) Keratinization and keratin pearl formation (H and E, 40x). (b) Nests of neoplastic squamous cells with pleomorphic, hyperchromatic, and vesicular nuclei. Prominent nucleoli and mitosis were also seen (H and E, x10)Figure 3: (a) Recurrence of the growth over the same site (Lower lip). (b) Complete regression of lesions after topical 5-fluorouracil 1% cream applicationCutaneous horns, also known as “Cornu cutaneum” in Latin, have been enigmatic rare entities, with an incidence of 0.3–1.3%. It develops as a result of hyperproliferation and increased cohesiveness of keratin due to an unknown mechanism. Sun exposure is the most important etiological factor in the pathogenesis of the cutaneous horn. However, poor oral hygiene and smoking may have an additional role in their development on the lips. It can arise from a variety of benign lesions (DLE, epidermal nevus, sebaceous adenoma, seborrheic keratosis, trichilemmoma, verruca vulgaris), premalignant lesions (actinic keratosis, arsenical keratosis, Paget’s disease, solar keratosis), and malignant lesions (squamous cell carcinoma, basal cell carcinoma, Bowen’s disease, Kaposi sarcoma, keratoacanthoma). The association of cutaneous horn with malignant or premalignant potential is found to be around 20–38.9%, with the squamous cell carcinoma being the most common histopathological variant owing to its increased association with keratin formation.[2] Cutaneous horns over mucosal sites are indeed rare. Table 1 shows previous case reports of cutaneous horn over mucosal sites.Table 1: Previous case reports of cutaneous horn over mucosal sitesDLE has very rarely been associated with a horn.[3,4] There are only two previous reports of malignant transformation at the base of the cutaneous horn over the lower lip.[5,6] Although there are no validated data on the prevalence and incidence of cutaneous horns occurring at the lower lip, which is considered to be an extremely rare location. A chronic scar, inflammation, ultraviolet radiation, and immunosuppressive medications are proposed explanations for the high risk of developing skin cancer in DLE. SCC has been reported in 2.3–3.3% of DLE patients, with substantially higher rates of recurrence and metastasis compared with sporadic SCC.[7] Recently cutaneous horns developing from pseudoepitheliomatous keratotic and micaceous balanitis have also been reported.[8,9] Our case is unique and rare in presentation on account of the co-existence of squamous cell carcinoma, cutaneous horn, and chronic DLE lesion in a rare location. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.