Brushing your teeth one morning, you discover a dark spot in the back of your mouth. Do you ignore it or have it removed?
Whether appearing in your mouth or on your lip, it is best to have unexplained oral pigment changes diagnosed by an Ear, Nose and Throat (ENT) specialist (otolaryngologist), which may require referral by a primary care physician, dermatologist or dentist. This is especially the case if there is no resolution or improvement within a week or two. 
Is the dark spot cancerous? The ambiguous "dark spot" description could elicit several etiologies. Painless flat brown, black, blue or gray colored spots can be hereditary (congenital nevus), occur as a result of smoking, or manifest spontaneously as a sudden melanogenesis, even in areas lacking sun exposure, where pigmentation is uncommon.
Melanotic macule is an oral equivalent of a freckle or brown pigmented patch of the skin. In children it is most likely racial in origin, in which case it may be called racial pigmentation or physiologic pigmentation with unnecessary treatment. Most oral melanotic macules are benign discolorations. However, recurring oral melanoses may actually represent the radial growth phase of oral melanoma in some instances.  Melanotic macules can also be present on gums or lips. 
Mucosal lentiginous melanomas (MLMs) develop from the mucosal epithelium that lines the respiratory, gastrointestinal, and genitourinary tracts. These lesions account for approximately 3% of the melanomas diagnosed annually and may occur on any mucosal surface, including the conjunctiva, oral cavity, esophagus, vagina, female urethra, penis, and anus. Noncutaneous melanomas commonly are diagnosed in patients of advanced age. MLMs appear to have a more aggressive course than cutaneous melanomas, although this may be because they commonly are diagnosed at a later stage of disease than the more readily apparent cutaneous melanomas. 
With fewer than 100 cases reported since first identified within the past century, oral melanaocanthoma is a rare condition characterized by a proliferation of both melanocytes and keratinocyes that results in pigmented or plaquelike lesions in the oral mucosa. 
Atypical melanocytic proliferation does not fit neatly within a defined dermapathology. There are established histopathologic criteria to make the distinction between a oncogenic invasive growth phase and a proliferative nodule such or congenital nevus (birthmark). However, there are inevitably transitional stages. 
Oral melanocytic nevus (pigmented nevus, nevocellular nevus) is essentially a benign mole in the mouth. This rare proliferation of pigment cells, occurring in 1/2,000 adults, produces brown or bluish dome-shaped or sessile mass, usually with a smooth surface. It should be biopsied to rule out melanoma. 
Though there are wide variety of causes for dark brown, blue or gray oral macules, a similar red one is likely the result of blunt-force trauma.  Red macules that do not resolve within a week or two may suggest epethelial dysplasia — microscopic alterations of epithelial cells and tissue from normal toward the appearance of cells and tissue usually seen in cancers arising from that epithelium. 
From an unaided visual examination, it is virtually impossible to distinguish between a benign melanotic macule or a mucosal lentiginous melanoma. In fact, non-cancerous melanotic macules are sometimes called mucosal lentigines. For this reason a qualified doctor may recommend a biopsy, which is actually an excision to remove all the pigmentation.  The skin is then examined microscopically to determine malignancy. If positive, the cause is already completely removed. If negative, it is possible to elucidate potential recurrence or oral atypical melanocytic proliferation. 
While some doctors prefer to monitor the size and appearance over time, most will likely err on the side of caution and recommend a biopsy (full excision) even with the overwhelming odds of a benign conclusion. A couple of weeks of discomfort is anticipated afterwards but most experts agree it is prudent to remove spontaneously occurring oral melanotic macules for histologic confirmation of clinical impressions. 
A physician may evaluate prior illnesses, macule growth history, predisposition to tobacco or alcohol and potential projectile genesis. Macule location may have a bearing on the decision to biopsy. Those on the cheek mucosa or hard palate could be excised and cauterized in under 30 minutes with a local anesthetic. A macule on the soft palate can trigger gag reflexes that necessitate more expensive anesthetized oral surgery. Either way, the oral mucosa resurfaces well. Labial macule removal or excision from gums will leave minimally temporary visible scaring that warrants cosmetic consideration and more thorough risk assessment.
Disclosure: At the time this article was written, the author had discovered a dark spot on the soft palate. This research led to agreement with the otolaryngologist recommendation for biopsy. Results were benign and the diagnosis was oral melanotic macule.
- Oral Melanotic Macule, MaxilloFacialCenter.com
- Oral Melanotic Macule, skinsight.com
- Malignant Melanoma, eMedicine from WebMD.com
- Oral Melanoacanthoma, eMedicine from WebMD.com
- Atypical melanocytic proliferation, not falling into a specific diagnostic category, DermpathMD.com
- Melanocytic Nevus, MaxilloFacialCenter.com
- Purpuric Macules of the Oral Cavity, SoftDental.com
- Epithelial Dysplasia of the Head & Neck, MaxilloFacialCenter.com
- Skin Biopsy, eMedicineHealth.com
- Buchner A, et al. Relative frequency of solitary melanocytic lesions of the oral mucosa J Oral Pathol Med. 2004 Oct; 33(9): 550-7
- The oral melanotic macule, Page LR, et al. Oral Surg Oral Med Oral Pathol. 1977 Aug;44(2):219-26, PubMed.gov
- Melanocyte, Wikipedia