Plantar Fibroma: This condition is characterized by a benign growth on the plantar fascia, which can cause pain and a palpable lump, especially when pressure is applied or during rest. The absence of insoles, which previously may have provided some relief, could exacerbate the symptoms.

Morton's Neuroma: A common condition that involves a thickening of the tissue around one of the nerves leading to the toes, causing pain and discomfort, especially when pressure is applied. The pain is typically localized and can be exacerbated by tight shoes or the absence of supportive insoles.
Bursitis: Inflammation of a bursa, a fluid-filled sac that cushions bones, tendons, and muscles near joints, can cause pain and swelling, especially with pressure or at rest. The location of the "lump" and the nature of the pain could suggest bursitis, particularly if the patient has a history of repetitive activities or trauma to the foot.
Plantar Fasciitis: Although typically associated with pain upon initial weight-bearing in the morning, plantar fasciitis could also cause pain at rest or with pressure if the condition is severe or if there are complicating factors such as a heel spur. The absence of supportive insoles could worsen symptoms.

Osteoid Osteoma: A benign bone tumor that can cause severe pain, often worse at night or with rest, and can be relieved by NSAIDs. Although rare, missing this diagnosis could lead to prolonged unnecessary pain and suffering.
Ewing's Sarcoma or Other Malignant Bone Tumors: Although extremely rare, these conditions can present with localized pain and swelling. Given the potential severity of these conditions, they must be considered in the differential diagnosis, especially if the pain is persistent, worsening, or accompanied by other systemic symptoms like fever or weight loss.
Infection (e.g., Abscess or Osteomyelitis): Infections can cause localized pain, swelling, and sometimes a palpable mass. These conditions require prompt diagnosis and treatment to prevent serious complications.

Gout or Pseudogout: These conditions involve the deposition of crystals within joints and can cause acute, severe pain and swelling. While they more commonly affect the big toe, they can occur in other parts of the foot and could potentially cause a "lump" if there is significant soft tissue involvement.
Foreign Body Reaction: If the patient has a history of stepping on something or a recent foot injury, a foreign body reaction could cause localized pain, swelling, and a palpable mass.
Neurofibroma: A benign nerve sheath tumor that can cause pain and a palpable lump, especially if it is pressing on surrounding structures.