Darkening and Eruptive Nevi During Treatment With Erlotinib

Eruptive nevi previously were reported in a patient who was treated with erlotinib.¹ Other tyrosine kinase inhibitors that also decrease signal transduction through the MAPK pathway, including sorafenib and vemurafenib, have been reported to cause eruptive nevi. There are 7 reports of eruptive nevi with sorafenib and 5 reports with vemurafenib.^7-9 Development of nevi were noted within a few months of initiating treatment with these medications.⁷

A PubMed search of articles indexed for MEDLINE using the terms erlotinib and melanoma and erlotinib and nevi yielded no prior reports of darkening of existing nevi or the development of melanoma during treatment with erlotinib. However, vemurafenib has been reported to cause dysplastic nevi, melanomas, and darkening of existing nevi, in addition to eruptive nevi.^8-10 The side effects of vemurafenib have been ascribed to a paradoxical upregulation of MAPK in BRAF wild-type cells. This effect has been well documented and demonstrated in vivo.^8,10 Perhaps erlotinib has a similar potential to paradoxically upregulate the MAPK pathway, thus stimulating cellular proliferation and survival.

Another tyrosine kinase receptor, c-KIT, is found on the cell membrane of melanocytes along with EGFR.^11,12 The c-KIT receptor also activates the MAPK pathway and is critical to the development, migration, and survival of melanocytes.^11,13 Stimulation of the c-KIT tyrosine kinase receptor also can induce melanocyte proliferation and melanogenesis.¹¹ The c-KIT receptor is encoded by the KIT gene (KIT proto-oncogene receptor tyrosine kinase). Mutations in this gene are associated with melanocytic disorders. Inherited KIT mutation leading to c-KIT receptor deficiency is associated with piebaldism. Acquired activating KIT mutations increasing c-KIT expression are associated with acral and mucosal melanomas as well as melanomas in chronically sun-damaged skin.¹³

We hypothesized that erlotinib-induced inhibition of the MAPK pathway could lead to a reactive increase in expression of c-KIT and thus stimulate melanocyte proliferation and pigment production. Similar feedback upregulation of an MAPK pathway stimulating receptor during downstream MAPK inhibition has been demonstrated in colon adenocarcinoma; in this setting, BRAF inhibitors blocking the MAPK pathway leads to upregulation of EGFR.­¹⁴ In our patient, c-KIT immunostaining revealed a mild to moderate increase in intensity (ie, the darkness of the staining) in nevi and melanomas during treatment with erlotinib compared to nevi biopsied before erlotinib treatment (Figure 2). The increased intensity of c-KIT immunostaining was further confirmed via semiquantitative digital image analysis. Using this method, a darkened nevus biopsied during treatment with erlotinib demonstrated 43.16% of cells (N=31,451) had very strong c-KIT staining, while a nevus biopsied before treatment with erlotinib demonstrated only 3.32% of cells (N=7507) with very strong c-KIT staining. Increased expression of c-KIT, possibly reactive to downstream inhibition the MAPK pathway from erlotinib, could be implicated in our case of eruptive nevi. 

In summary, we report a rare case of darkening of existing nevi and development of melanoma in situ during treatment with erlotinib. The patient’s therapeutic timeline and concurrence of other well-documented side effects provided support for erlotinib as the causative agent in our patient. Additional support is provided through reports of other medications affecting the same pathway as erlotinib causing eruptive nevi, darkening of existing nevi, and melanoma in situ.^7-10 Through c-KIT immunostaining, we demonstrated that increased expression of c-KIT might be responsible for the changes in nevi in our patient. We, therefore, suggest frequent full-body skin examinations in patients treated with erlotinib to monitor for the possible development of malignant melanomas.