Definitive diagnosis of Merkel cell carcinoma (MCC) requires examination of biopsy tissue. An ideal biopsy specimen is either a punch biopsy or a full-thickness incisional biopsy of the skin including full-thickness dermis and subcutaneous fat. In addition to standard examination under light microscopy, immunohistochemistry (IHC) is also generally required to differentiate MCC from other morphologically similar tumors such as small cell lung cancer, the small cell variant of melanoma, various cutaneous leukemic/lymphoid neoplasms, and Ewing's sarcoma. Similarly, most experts recommend longitudinal imaging of the chest, typically a CT scan, to rule out that the possibility that the skin lesion is a cutaneous metastasis of an underlying small cell carcinoma of the lung.

Diagnosis is confirmed via biopsy of the tissue(s) suspected to be affected by SCC. For the skin, look under skin biopsy.

The pathological appearance of a squamous cell cancer varies with the depth of the biopsy. For that reason, a biopsy including the subcutaneous tissue and basalar epithelium, to the surface is necessary for correct diagnosis. The performance of a shave biopsy (see skin biopsy) might not acquire enough information for a diagnosis. An inadequate biopsy might be read as actinic keratosis with follicular involvement. A deeper biopsy down to the dermis or subcutaneous tissue might reveal the true cancer. An excision biopsy is ideal, but not practical in most cases. An incisional or punch biopsy is preferred. A shave biopsy is least ideal, especially if only the superficial portion is acquired.

Basal-cell carcinoma is a common skin cancer and occurs mainly in fair-skinned patients with a family history of this cancer. Sunlight is a factor in about two-thirds of these cancers; therefore, doctors recommend sunscreens with at least SPF 30. One-third occur in non-sun-exposed areas; thus, the pathogenesis is more complex than UV exposure as "the" cause.

The use of a chemotherapeutic agent such as 5-Fluorouracil or imiquimod, can prevent development of skin cancer. It is usually recommended to individuals with extensive sun damage, history of multiple skin cancers, or rudimentary forms of cancer (i.e., solar keratosis). It is often repeated every 2 to 3 years to further decrease the risk of skin cancer.

The following methods are employed in the treatment of basal-cell carcinoma (BCC):

The long-term outcome of squamous cell carcinomas is dependent upon several factors: the sub-type of the carcinoma, available treatments, location(s) and severity, and various patient health-related variables (accompanying diseases, age, etc.). Generally, the long-term outcome is positive, as less than 4% of Squamous cell carcinoma cases are at risk of metastasis. Some particular forms of squamous cell carcinomas have a higher mortality rate. One study found squamous cell carcinoma of the penis had a much greater rate of mortality than some other forms of squamous cell carcinoma, that is, about 23%, although this relatively high mortality rate may be associated with possibly latent diagnosis of the disease due to patients avoiding genital exams until the symptoms are debilitating, or refusal to submit to a possibly scarring operation upon the genitalia. Squamous cell carcinoma occurring in the organ transplant population is also associated with a higher risk of mortality.

Carcinomas can be definitively diagnosed through biopsy, including fine-needle aspiration (FNA), core biopsy, or subtotal removal of single node. Microscopic examination by a pathologist is then necessary to identify molecular, cellular, or tissue architectural characteristics of epithelial cells.

This type of cancer occurs most often in Caucasians between 60 and 80 years of age, and its rate of incidence is about twice as high in males as in females. There are roughly 1,500 new cases of MCC diagnosed each year in the United States, as compared to around 60,000 new cases of melanoma and over 1 million new cases of nonmelanoma skin cancer. MCC is sometimes mistaken for other histological types of cancer, including basal cell carcinoma, squamous cell carcinoma, malignant melanoma, lymphoma, and small cell carcinoma, or as a benign cyst. Researchers believe that exposure to sunlight or ultraviolet light (such as in a tanning bed) may increase the risk of developing this disease. Similar to melanoma, the incidence of MCC in the US is increasing rapidly.

Immunosuppression can profoundly increase the odds of developing Merkel-cell carcinoma. Merkel-cell carcinoma occurs 30 times more often in people with chronic lymphocytic leukemia and 13.4 times more often in people with advanced HIV as compared to the general population; solid organ transplant recipients have a 10-fold increased risk compared to the general population.

While cancer is generally considered a disease of old age, children can also develop cancer. In contrast to adults, carcinomas are exceptionally rare in children..

The two biggest risk factors for ovarian carcinoma are age and family history.

Photodynamic therapy, cryotherapy (freezing), or local chemotherapy (with 5-fluorouracil) are favored by some clinicians over . Because the cells of Bowen's disease have not invaded the dermis, it has a much better prognosis than invasive squamous cell carcinoma.

Good results have been noted with the use of imiquimod for Bowen's disease, including on the penis (erythroplasia of Queyrat), although imiquimod is not (as of 2013) approved by the U.S. Food and Drug Administration for the treatment of any type of squamous cell carcinoma, and serious side effects can occur with use of imiquimod.

Prognosis can range considerably for patients, depending where on the scale they have been staged. Generally speaking, the earlier the cancer is diagnosed, the better the prognosis. The overall 5-year survival rate for all stages of penile cancer is about 50%.

This type of carcinoma is commonly managed by local resection, cryotherapy, topical chemotherapy, and radiotherapy. Multimodal therapy has been shown to improve both visual prognosis and survival.

Mohs micrographic surgery has become the treatment of choice for this form of cancer. When used as the primary treatment modality for sebaceous carcinoma of the eyelid, Mohs surgery is associated with significantly lower local and distant recurrence rates.

The prognosis varies dramatically, depending on the type and stage at the time of treatment. However, the most common epitheliomas are very easily treated and rarely result in death.

Recurrence is common, although the recurrence rates for block resection followed by bone graft are lower than those of enucleation and curettage. Follicular variants appear to recur more than plexiform variants. Unicystic tumors recur less frequently than "non-unicystic" tumors. Persistent follow-up examination is essential for managing ameloblastoma. Follow up should occur at regular intervals for at least 10 years. Follow up is important, because 50% of all recurrences occur within 5 years postoperatively. Recurrence within a bone graft (following resection of the original tumor) does occur, but is less common. Seeding to the bone graft is suspected as a cause of recurrence. The recurrences in these cases seem to stem from the soft tissues, especially the adjacent periosteum. Recurrence has been reported to occur as many as 36 years after treatment.

To reduce the likelihood of recurrence within grafted bone, meticulous surgery with attention to the adjacent soft tissues is required.

Treatment usually involves surgically removing the tumor and affected tissue. Also used cryosurgery and radiotherapy.

When associated with the prostate, squamous cell carcinoma is very aggressive in nature. It is difficult to detect as there is no increase in prostate specific antigen levels seen; meaning that the cancer is often diagnosed at an advanced stage.

a) Surgical resection is mainstay of treatment, whenever possible. If tumor is completely removed, post-operative radiation therapy is typically not needed since acinic cell is considered a low-grade histology. Post-operative radiation therapy for acinic cell carcinoma is used if: 1) margins are positive, 2) incomplete resection, 3) tumor invades beyond gland, 4) positive lymph nodes.

b) Neutron beam radiation

c) Conventional radiation

d) Chemotherapy

PUNLMPs are exophytic lesions that appear friable to the naked eye and when imaged during cystoscopy.

They are definitively diagnosed after removal by microscopic examination by pathologists.

Histologically, they have a papillary architecture with slender fibrovascular cores and rare basal mitoses. The papillae rarely fuse and uncommonly branch. Cytologically, they have uniform nuclear enlargement.

They cannot be reliably differentiated from low grade papillary urothelial carcinomas using cytology, and their diagnosis (vis-a-vis low grade papillary urothelial carcinoma) has a poor inter-rater reliability.

Pathologic grading and staging tumors are:

graded by the degree of cellular atypia (G1->G3), and

staged:

It is important to exclude a tumor which is directly extending into the ear canal from the parotid salivary gland, especially when dealing with an adenoid cystic or mucoepidermoid carcinoma. This can be eliminated by clinical or imaging studies. Otherwise, the histologic differential diagnosis includes a ceruminous adenoma (a benign ceruminous gland tumor) or a neuroendocrine adenoma of the middle ear (middle ear adenoma).

PUNLMPs are treated like non-invasive low grade papillary urothelial carcinomas, excision and regular follow-up cystoscopies.

There is a rare occurrence of a pelvic recurrence of a low-grade superficial TCC after cystectomy. Delayed presentation with recurrent low-grade urothelial carcinoma is an unusual entity and potential mechanism of traumatic implantation should be considered. Characteristically low-grade tumors are resistant to systemic chemotherapy and curative-intent surgical resection of the tumor should be considered.

Human papillomavirus infection (HPV) has been associated with SCC of the oropharynx, lung, fingers and anogenital region.

Sunscreen is effective and thus recommended to prevent melanoma and squamous-cell carcinoma. There is little evidence that it is effective in preventing basal-cell carcinoma. Other advice to reduce rates of skin cancer includes avoiding sunburning, wearing protective clothing, sunglasses and hats, and attempting to avoid sun exposure or periods of peak exposure. The U.S. Preventive Services Task Force recommends that people between 9 and 25 years of age be advised to avoid ultraviolet light.

The risk of developing skin cancer can be reduced through a number of measures including decreasing indoor tanning and mid day sun exposure, increasing the use of sunscreen, and avoiding the use of tobacco products.

There is insufficient evidence either for or against screening for skin cancers. Vitamin supplements and antioxidant supplements have not been found to have an effect in prevention. Evidence for a benefit from dietary measures is tentative.

Zinc oxide and titanium oxide are often used in sun screen to provide broad protection from UVA and UVB ranges.

Eating certain foods may decrease the risk of sunburns but this is much less than the protection provided by sunscreen.

Prognosis is good for acinic cell carcinoma of the parotid gland, with five-year survival rates approaching is 90%, and 20-year survival exceeding 50%. Patients with acinic cell carcinomas with high grade transformation (sometimes also called dedifferentiation) have significantly worse survival.

The prognosis of an acinic cell carcinoma originating in the lung is much more guarded than cases of this rare histotype occurring in most other organs, but is still considerably better than for other types of lung cancer.

Overall, five-year survival rates for vulvar cancer are around 78% but may be affected by individual factors including cancer stage, cancer type, patient age and general medical health. Five-year survival is greater than 90% for patients with stage I lesions but decreases to 20% when pelvic lymph nodes are involved. Lymph node involvement is the most important predictor of prognosis. Thus, early diagnosis is important.

Other cancerous lesions in the differential diagnosis include Paget's disease of the vulva and vulvar intraepithelial neoplasia (VIN). Non-cancerous vulvar diseases include lichen sclerosus, squamous cell hyperplasia, and vulvar vestibulitis. A number of diseases cause infectious lesions including herpes genitalis, human papillomavirus, syphilis, chancroid, granuloma inguinale, and lymphogranuloma venereum.

Some tests which detect cancer could be called "screening for epithelial dysplasia". The principle behind these tests is that physicians expect dysplasia to occur at the same rate in a typical individual as it would in many other people. Because of this, researchers design screening recommendations which assume that if a physician can find no dysplasia at certain time, then doing testing before waiting until new dysplasia could potentially develop would be a waste of medical resources for the patient and the healthcare provider because the chances of detecting anything is extremely low.

Some examples of this in practice are that if a patient whose endoscopy did not detect dysplasia on biopsy during screening for Barrett's esophagus, then research shows that there is little chance of any test detecting dysplasia for that patient within three years.

Individuals at average-risk for colorectal cancer should have another screening after ten years if they get a normal result and after five years if they have only one or two adenomatous polyps removed.