Immunohistochemistry p40+ represents a positive finding of p40 protein by immunohistochemical method of antigen-antibody reaction. p40 is considered to be the squamous cell carcinoma marker with the highest sensitivity and specificity, and is often positive in squamous carcinoma. Immunohistochemistry is a method that uses antigen-antibody reaction to identify peptides, proteins and other markers in the cell membrane, cell nucleus and cell plasma, which is commonly used in the diagnosis of tumors, and it can help to determine the source of the tumor cells and determine the site of origin of the tumors. For example, when some tumor cells are judged to be malignant by microscopic examination, but when the specific source of the cells is not clearly identified, immunohistochemistry can be applied to help to determine the source of the tumor cells. p40 is a relatively sensitive and specific protein localized in the nucleus of squamous cell carcinoma, which is one of the most commonly used markers for squamous lung carcinoma, and is hardly expressed in other pathological types such as lung adenocarcinoma, so it is often used in differential diagnosis of squamous lung carcinoma; besides p40, immunohistochemical indexes such as p63, CK5/6, and so on are often expressed in squamous cell carcinoma, which are often used together with p40 for the differentiation of squamous carcinoma from other pathological types. Therefore, p40+ represents positive p40 protein, which may be related to squamous cell carcinoma. The specific significance of p40 needs to be combined with common HE staining and other immunohistochemical indexes to make a comprehensive judgment, and it is suggested that patients should interpret and analyze the indexes under the guidance of doctors.